LIBRARY 

OF  THE 

UNIVERSITY  OF  CALIFORNIA. 


Class 


or  THE 
UNIVERSITY 

OF 


2o'  X  120'  STAND-PIPE,  ST.  AUGUSTINE,  FLA. 


Frontispiece. 


TOWERS    AND    TANKS 

FOR 

WATER-WORKS. 

THE  THEORY  AND  PRACTICE  OF  THEIR 
DESIGN  AND   CONSTRUCTION. 


BY 


J.    N.    HAZLEHURST, 


Member  of   the  American    Society    of  Civil  Engineers;    Member   of  the   Society   for  Municipal 
Improvement;    Member  American    Water-works  Association. 


THIRD  EDITION,    REVISED  AND   ENLARGED. 
FIRST    THOUSAND. 


OF    THE 

UNIVERSITY 

OF 


NEW  YORK: 
JOHN   WILEY   &   SONS. 

LONDON:    CHAPMAN  &   HALL,   LIMITED. 
1907. 


Copyright,  1901,  1904, 

BY 
J.  N.   HAZLEHURST. 


ROBERT   DRUMMOND.    PR1KTER,    NEW  YOR1 


INTRODUCTION. 


IT  is  a  strange  fact  to  chronicle  that,  amongst  the  great  mass 
of  scientific  literature,  there  is  no  distinct  treatise  upon  the  design 
and  construction  of  metallic  receptacles  or  structures  whose 
province  it  is  to  retain  a  sufficient  reserve  supply  of  water,  elevated 
to  a  proper  height  and  intended  to  be  used  in  conjunction  with 
other  necessary  features  of  a  modern  water-supply  system.  Such 
structures,  generally  termed  "  tanks,"  "  water-towers,"  " stand- 
pipes,"  or  "towers  and  tanks,"  according  to  their  design,  are 
rapidly  increasing  in  number,  and  are  being  generally  specified 
in  the  smaller  water-plants,  where  the  economies  are  to  be  prac- 
tised and  natural  and  suitable  elevations  are  unattainable.  The 
popularity  of  this  class  of  reservoir  being  on  the  increase,  it  would 
seem  that  along  with  the  many  exhaustive  and  elaborate  discus- 
sions of  kindred  subjects,  as  hydraulics,  hydrostatics,  statics, 
stress,  and  the  metallurgy  and  physical  properties  of  structural 
steel,  there  might  be  found  some  work  dealing  with  this  now 
important  subject,  but  so  far  as  the  writer  is  aware,  in  the  entire 
range  of  such  productions,  only  the  most  fragmentary  articles 
are  to  be  found. 

The  inability  to  procure  definite  or  reliable  information  upon 
the  design  and  construction  of  such  work  is  probably  the  cause 
of  the  scanty  and  meagre  instructions  frequently  appearing  in 
sets  of  specifications  for  water- works  construction,  and  the  defi- 
ciency in  this  respect  has  been,  commented  upon  by  a  prominent 
member  of  the  profession  in  the  following  terms: 

iii 


195052 


IV  INTRODUCTION, 

"The  custom  has  been,  to  a  greater  extent  than  in  any  other 
engineering  work  of  like  importance,  to  buy  a  stand-pipe  much  as 
a  barrel  of  flour  would  be  bought;  the  contract  or  agreement 
would  be  for  a  stand-pipe  so  high  and  so  wide,  the  material  and 
workmanship  to  be  first  class  in  every  respect." 

Without  previous  experience,  and  unable  to  secure  any  degree 
of  exact  information  as  to  the  best  practice  for  stand-pipe  design, 
it  would  be  amusing,  if  not  so  serious  a  matter,  to  compare  the 
emaciated  paragraph,  its  stock  phrases  and  blanket  clauses,  so 
lax  that  any  "  rule-of -thumb "  boiler- maker  can  safely  provide 
almost  anything  in  the  shape  of  a  tank,  provided  it  holds  together 
and  does  not  leak  too  badly,  with  the  plethoric  clause,  wasting 
much  good  paper  and  printer's  ink  in  padding  the  specifications 
to  give  an  important  appearance  to  the  technical  description 
dealing  with  requirements  for  "cast-iron  pipe,"  which  probably 
gets  its  first  inspection  when  the  pressure  is  applied  from  the 
pumping -engines. 

Observing  this  condition  of  affairs,  and  having  experienced 
personally  the  difficulties  to  be  encountered  in  securing  data  for 
work  of  this  sort,  during  the  year  1901  the  writer  published  the 
first  edition  of  this  volume.  Its  reception  seemed  to  show  a 
reason  for  its  appearance  and  a  demand  for  a  second  edition. 
Profiting  by  the  criticisms  of  the  first  venture,  eliminations  have 
been  made,  typographical  and  other  errors  have  been  corrected, 
the  work  throughout  has  been  largely  revised  and  rewritten  and 
many  new  illustrations  have  been  added.  The  new  matter 
includes  a  record  of  stand-pipe  failures,  continuing  from  the 
time  of  Prof.  Pence's  monograph  to  the  present ;  a  comprehensive 
chapter  dealing  with  the  stresses  in  a  steel  water-tower,  originally 
presented  in  the  "Technograph,"  and  revised  and  rewritten  by 
Its  author  for  this  work;  also  two  chapters  upon  the  subject  of 
Specifications  for  and  the  Architectural  and  Ornamental  possi- 
bility of  Water-tower  Design. 

Necessarily  a  great  portion  of  such  production  as  this  must 


INTRODUCTION.  V 

be  compiled  from  the  experience  and  work  of  others,  and  to  all 
who  have  thus  contributed  the  author  desires  and  has  intended 
to  give  due  credit. 

Without  further  explanation,  this  second  edition  of  the  original 
work  is  offered  for  what  it  is  worth,  and  the  hope  is  expressed 
that  it  may  prove  of  some  service. 


CONTENTS. 


PAGB 

INTRODUCTION.  .  iii 


CHAPTER  I. 

HISTORICAL  :   EXPLANATORY  AND  STATISTICAL I 

Brief  Mention  of  Ancient  and  Modern  Works — Methods  of  Distri- 
bution— Reservoir  System  Discussed — Introduction  of  Metallic 
Reservoirs — Present  Extent  and  Character — Excentricity  of  Design — 
Tendency  of  Modern  Practice — Record  of  Failures. 


CHAPTER  II. 

THE  CHEMICAL  AND  PHYSICAL  PROPERTIES  OF  STRUCTURAL  METAL.    33 

Wrought  Iron — Physical  Difference  between  Iron  and  Steel — Effect 
of  Heating — Bessemer  Steel— Open -hearth  Steel— Effects  of  Phos- 
phorus— Manufacturers'  Standard  Specifications — Work  of  Inter- 
national Association. 


CHAPTER  III. 

STRUCTURAL  METALS 50 

The  Use  of  Iron — The  Change  to  Steel — Classification  of  Failures — 
Relative  Merits — Comparative  Cost — Comparative  Homogeneity 
and  Strength  of  Bessemer  and  Open-hearth  Steels — Suitable  Grades 
for  Structural  Work — Distinguishing  Terms— Chemical  Specifica- 
tions— Inspection. 

vii 


VUl  CONTENTS. 

CHAPTER  IV. 

PAGB 

STRESS  OR  STRAIN,  AND  STABILITY  OF  STRUCTURE 79 

Moment  of  Forces — Equilibrium — Resistance  to  Overturning — 
Wind-pressure  —  Hydrostatic  Pressure  —  Resistance  Offered  by 
Material. 

CHAPTER  V. 

MECHANICAL  PRINCIPLES 100 

Stresses — Bending  and  Resisting  Moments — Modulus  of  Elas- 
ticity— Radius  of  Gyration — The  Gordon  Formula  for  Strength  of 
Columns — Straight-line  Compression  Formula. 

CHAPTER  VI. 

THE  STRESSES  IN  A  STEEL  WATER-TOWER 109 

Gravity  Stress  —  Nomenclature  —  Stresses  in  the  Cylinder  — 
Stresses  in  the  Cone — Stresses  in  the  Segment  of  a  Sphere — 
Stresses  in  the  Joint  Eetween  the  Bottom  and  the  Cylinder — 
Stresses  in  the  Circular  Girder — Stresses  in  the  Posts — Stresses 
Resulting  from  the  Horizontal  Thrust  at  the  Top  of  the  Posts — 
Stresses  in  Ring  at  Top  of  Posts — Horizontal  Stresses  in  Plane  of 
Change  of  Inclination  of  Posts — Horizontal  Stresses  at  the  Base 
of  the  Tower — Wind-stresses — In  Cylinder — In  Tower — Loads  on 
the  Foundations — Conclusions. 

CHAPTER  VII. 

RIVETING 142 

Efficiency  of  Riveted  Joint — Single-riveted  Joint — Double-riveted 
Joint — Triple-riveted  Joint — Double-welt  Butt-joint — Pitch  of  Rivets 
— Size  of  Rivets  in  Relation  to  Thickness  of  Plates — Rivet  Sizes  and 
Spacing  for  Structural  Work. 

CHAPTER  VIII. 

DESIGNING 162 

Strain-sheet — Application  of  Mechanical  Principles — Thickness 
of  Plate — Joint  Efficiency — Bed-plate  and  Connection — Details — 
Method  of  Anchorage. 


CONTENTS.  IX 


CHAPTER  IX. 

PAGB 

DESIGNING — CONTINUED 177 

General  Considerations — Fairhaven  Failure— Consideration  of 
Tank  Bottom  and  Connections — The  Circular  Girder— Supporting 
Tower— Tank  Cover— Trolley  Rail— Ladder— Balcony— Supply 
Pipe — Frost-proofing — Connections — Wind-bracing — Anchorage — 
Graphic  Design — Estimating  Quantities — Stress  in  the  Girder — 
Wind  Stress  in  the  Girder — Tortion  Moment — Horizontal  Reaction 
at  the  Top  of  Posts — Overturning  Moments  at  Point  of  Support- 
Tension  in  the  Joint  Between  the  Bottom  and  the  Cylinder— Stress 
and  Section  of  Tower  Members— Bearing- plates— Stability  of 
Structure  and  Anchorage. 

CHAPTER  X. 

FOUNDATIONS 220 

9  Explanations — Rock — Clay — Dry    Sand — Quicksand — Increasing 

Bearing  Values — Stone  Masonry— Rankine's  Rule — Brick  Masonry 
— Concrete  Foundations— Maximum  Pressures — Designing  Founda- 
tions, including  Anchorage  and  Capping. 

CHAPTER  XI. 

PAINTING 243 

Discussion — Iron  Rust — Chemical  and  Galvanic  Action — Mill- 
scale — Cleaning  the  Metal— Zinc  coating—  ''Oxidized  "  Plates  — 
"  Japanned"  Plates — Practical  Considerations— Paint-films — Lin- 
seed-oil— Pigments — Red  Oxide  of  Lead — Asphallic  Varnish — 
Application — Repainting — Protective  Coverings  for  Iron  and  Steel — 
Average  Surface  Covered  per  Gallon  of  Paint. 

CHAPTER  XII. 

SHOP  PRACTICE  AND  ERECTION 270 

Laying  Out  Work — Machining — Punching  and  Rolling — Shop 
Assembly — Cleaning  and  Priming— Preparation  of  Foundations- 
Preliminaries  to  Erection  of  Stand  pipes— Field  Assembly  — Inspec- 
tion— Erection  of  Towers  and  Tanks — Field -rivet  ing — Machine- 
driven  Rivets. 


X  CONTENTS. 

CHAPTER  XIII. 

PAGE 

SPECIFICATIONS 289 

General  Discussion — Suggested  Form  for  Steel  Water-tower — 
Details — Materials — Inspection — Stresses — Shop  Work — Field  As- 
sembly— Test — Painting — Delay  in  Completion — Recommendations. 

CHAPTER  XIV. 

ARCHITECTURE  AND  ORNAMENTATION 310 

Opportunity  for  Architectural  Effect— Tendency  Toward  Orna- 
mentation— The  True  and  Beautiful  in  Architecture — Incongruous 
Architecture— Competitive  Water-tower  Designs— Recent  Examples 
of  Ornamented  Water-towers— The  Possibility  of  Architectural 
Effect  in  Structural  Metal  Design— Conspicuous  Examples. 


TOWERS  AND  TANKS   FOR  WATER-WORKS. 


CHAPTER    I. 
BRIEF   MENTION   OF   ANCIENT   AND   MODERN   WORKS. 

AMONGST  the  earliest  evidences  of  a  prior  civilization, 
ruined  aqueducts,  varying  in  design  and  extent,  indicate  the 
appreciated  necessity  of  public  water-supply  for  populous  com- 
munities. During  the  reign  of  the  Jewish  King,  Solomon, 
extensive  reservoirs  or  pools  were  designed  and  constructed, 
which  to  the  present  time  bear  his  name  and  testify  to  the 
wisdom  accredited  him,  continuing,  after  the  lapse  of  ages, 
to  deliver  a  supply  of  pure  water  to  the  citizens  of  Jerusalem. 

The  important  works  constructed  under  the  Caesars  present 
a  good  example  of  the  excellence  attained  by  the  hydraulician 
and  the  general  requirements  in  the  matter  of  water-supply  of 
that  day,  whilst  in  the  New  World,  amid  the  wreck  of  a  more 
remote  antiquity,  are  to  be  found  examples  of  the  genius  of  that 
mysterious  race,  the  Aztec,  and  its  application  toward  the 
development  of  this  most  important  factor  in  the  progress  of 
nations. 

Recognizing  and  putting  into  practical  use  the  principles 
of  the  great  natural  law  of  the  flow  of  liquids  impelled  by 
gravity,  convenient  mountain  streams  and  brooks  were  im- 
pounded and  led  down  the  hillsides  by  open  channels  or  aque- 
ducts for  the  convenience  of  the  people. 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 

In  scope  such  works  were  necessarily  limited  by  topograph- 
ical conditions,  and  permitted  only  the  application  of  the 
principles  governing  what  is  to-day  known  as  "The  Gravity 
System." 

For  centuries  this  method  of  water-distribution  prevailed, 
varied  and  modified  to  suit  different  conditions,  but  being 
shorn  from  time  to  time  of  original  crudities,  and  participating 
in  the  general  advance  toward  a  higher  civilization,  the  system 
has  reached  a»  high  degree  of  efficiency. 

The  wonderful  advancement  of  the  present  epoch  in  scien- 
tific knowledge  and  mechanical  development  has  made  possible 
the  economical  production  and  transmission  of  power,  along 
with  which  has  come  the  knowledge  of,  necessity  for,  and  ad- 
vantage to  be  derived  from  the  employment  of  mechanical 
means  and  methods  for  the  accomplishment  of  required  results 
by  other  than  the  primitive  principles  of  gravity  flow. 

The  reference  to  advantages  to  be  derived  from  the  em- 
ployment of  artificial  methods  as  applied  to  water-distribution, 
rather  than  the  utilization  of  natural  agencies,  is  relative,  and 
is  intended  to  apply  only  to  a  broadening  of  the  possibilities; 
for  in  the  consideration  of  the  question  of  general  or  particu- 
lar source  of  water-supply,  the  first  investigation  should  deal 
with  the  possibility  of  procuring  a  gravity  flow,  and  all  sub- 
sequent- propositions  should  be  referred  to  the  cardinal  princi- 
ple and  initial  hypothesis  that  for  economy,  efficiency,  and 
consequent  desirability,  Nature's  methods  take  precedence 
over  mechanical  means. 

Methods  of  Distribution. — Since  the  application  of  scien- 
tific methods  to  natural  forces,  the  problem  of  water-distribu- 
tion may  be  broadly  separated  into  three  general  schemes  or 
systems — "The  Gravity,"  "The  Reservoir,"  and  "The  Di- 
rect"— each  showing  particular  advantage  in  individual  cases. 

Of  the  first  of  these,  for  the  purposes  of  this  discussion, 
possibly  enough  has  been  said. 


ANCIENT  AND    MODERN    WORKS.  3 

The  second,  under  a  multiplicity  of  design,  has  for  its 
object  the  mechanical  elevation  of  water  from  a  lower  to  a 
higher  level,  and  its  storage  in  basins  or  reservoirs  of  sufficient 
size  and  elevation  to  answer  all  of  the  requirements. 

The  third,  or  "  Direct,"  scheme  distributes  the  water  by  a 
constant,  applied  mechanical  pressure  to  the  contemplated 
points  of  delivery.  In  this  monograph,  a  subdivision'  of  the 
second  of  these  broad  methods  will  be  discussed,  as  its  scope 
is  intended  to  cover  the  architectural  design ;  materials  and 
methods  of  constructing  and  erecting  elevated  storage-reser- 
voirs, which  of  late  years  have  played  an  important  part  in  the 
general  economy  of  most  water-works  designs. 

Reservoir  System  Discussed.— The  detail  of  such  con- 
struction is  subject  to  local  condition,  and  ranges  from  designs 
for  small  tanks  elevated  upon  supporting  columns  to  immense 
reservoirs  for  the  water-supply  of  great  cities.  In  the  general 
scheme  of  a  water-supply  system  the  elevated  reservoir  serves 
a  dual  purpose ;  providing  for  a  surplus  supply  to  be  utilized 
as  required,  as  well  as  permitting  a  temporary  suspension  of 
the  mechanical  operations  of  the  plant ;  its  further  purpose  is 
its  ability  to  relieve  internal  pressures,  acting  in  this  capacity 
as  a  regulator  or  relief-valve  to  the  entire  system  of  distribu- 
tion. Considered  simply  as  a  receptacle  for  elevated  storage, 
its  purpose  and  principles  are  obvious. 

In  the  natural  exercise  of  the  functions  of  an  automatic 
safety-valve,  the  results  are  similar  to  those  produced  by  an 
air-chamber,  closely  connected  to  the  pumping  machinery. 
The  force  exerted  in  the  intermittent  action  of  an  enclosed 
column  of  water  compressed  or  impelled  by  the  forward  move- 
ment of  the  pistons  or  plungers  of  the  pumping-engine,  acts 
as  a  "  ram,"  producing  rupture,  according  to  the  intensity  of 
the  force  exerted,  to  pipe-mains,  connections  and  joints. 
This  stress  may  be  relieved  and  the  shock  regulated  by  pro- 
viding for  a  discharge  of  the  water  under  pressure  into  an 


4  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

open  reservoir  whose  upper  or  highest  elevation  shall  be  some- 
what in  excess  of  the  height  to  which  the  water  would  natur- 
ally be  forced  under  the  stress  conditions,  otherwise  the 
reservoir  will  overflow. 

Whilst  this  destructive  tendency  has  been  greatly  lessened 
by  the  use  of  improved  duplex  pumping  machinery,  there  is 
also  to"  be  considered  in  the  economy  of  operation  a  certain 
loss  of  energy  due  to  the  force  necessary  to  put  in  motion  the 
column  of  water,  temporarily  suspended  at  the  expiration  of 
each  forward  stroke  of  the  machinery  by  the  rigid  enclosing 
sides  of  the  pipe-lines.  Connections  to  an  open  reservoir  pro- 
vide an  opportunity  for  escape  and  permits  an  onward  move- 
ment of  the  liquid  column,  relieving  the  "  back  pressure," 
and,  through  its  own  momentum,  effecting  a  saving  in  energy 
necessary  to  impel  it  forward.  The  relief  to  the  pipe  system 
is  to  the  same  extent  enjoyed  by  the  pumping  machinery,  re- 
ducing the  strains  upon  the  mechanism  and  the  consequent 
number  and  extent  of  repairs,  and,  more  important  still,  the 
liability  to  accident  at  some  critical  moment.  Any  open  res- 
ervoir or  vertical  pipe,  of  whatever  diameter  and  of  sufficient 
height,  will  afford  the  desired  relief,  but  it  is  the  usual  practice 
to  couple  with  this  desideratum  a  capacity  sufficient  for  a  re- 
serve supply. 

The  accomplishment  of  these  requirements  is  generally 
secured  for  the  larger  cities  by  reservoirs  of  earth  and  masonry 
construction  for  reasons  of  economy  and  permanency,  and 
designed  to  suit  topographical  conditions  and  local  demands. 

For  the  same  reasons,  in  all  preliminary  investigations  for 
the  water-supply  of  the  smaller  cities  and  towns,  elevated  sites 
suitable  for  similar  construction  should  be  sought  and  first 
given  careful  consideration. 

The  subject  of  the  theory,  details,  and  construction  of  such 
reservoirs  has  been  discussed  by  such  eminent  authorities,  and 
so  great  a  volume  of  scientific  and  prolix  literature  has  been 


ANCIENT  AND    MODERN  WORKS.  $ 

devoted  to  its  consideration,  that  no  attempt  will  be  made 
here  to  introduce  original  conclusions,  owing  to  the  unlikeli- 
hood of  the  author  being  able  to  add  anything  worthy  of  re- 
ceiving consideration. 

Introduction  of  Metallic  Reservoirs  in  the  United  States. — 
The  historic  record  of  the  introduction  of  metallic  reservoirs, 
if  procurable,  would  be  of  much  general  interest,  but  unfor- 
tunately such  information  is  of  the  most  meagre  and  unsatis- 
factory character;  of  more  or  less  doubtful  authenticity. 

The  oldest  complete  water  system  installed  in  the  United 
States  is  believed  to  be  that  erected  at  Bethlehem,  Pennsyl- 
vania, in  1754-61,  by  Hans  Christopher  Christiansen,  at  which 
point  two  stand-pipes  have  at  different  times  been  constructed. 
The  first  of  these,  a  tank 40  X  24ft.  with  a  capacity  of  225,000 
gallons,  having  served  its  term  of  usefulness,  was  abandoned, 
and  a  new  steel  structure  replaces  it. 

Mr.  R.  E.  Neumeyer,  superintendent,  writes  that  for  some 
time  he  has  been  engaged  in  procuring  data  as  to  the  history 
of  this  plant,  and  this  he  intends  giving  publicity  later,  which, 
it  is  to  be  hoped,  he  will. 

In  a  recent  volume  of  the  Engineering  News  there  appears 
a  brief  article  mentioning  a  stand-pipe  erected  in  the  city  of 
New  York,  by  or  through  the  instrumentality  of  Aaron  Burr, 
in  connection  with  the  launching  of  the  Manhattan  Company, 
a  banking  house,  chartered  1/99,  and  in  existence  at  this  time. 
The  tank  is  described  as  about  35  ft.  in  diameter  by  15  ft. 
in  height,  composed  of  segmental  courses  of  iron  castings, 
with  flanged  and  bolted  joints.  Each  segment  is  2\  ft.  wide 
by  5  ft.  high,  re-enforced  by  a  web,  midway,  the  flanges  at 
the  joints  being  also  re-enforced  by  web  angles.  An  orna- 
mental effect  is  obtained  by  beads  forming  panels  on  each 
half  of  the  outer  facings  of  the  segmental  castings.  Four 
iron  hoops  are  placed  around  the  tank,  and  the  structure  is 
supported  by  a  masonry  tower  some  15  or  20  ft.  in  height. 


O  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

The  supply-pipe  is  20  ins.  in  diameter,  and  is  provided 
with  a  gate,  enclosed  in  a  rectangular  chamber,  formed  by 
bolting  together  two  flanged  iron  castings.  The  following  has 
been  subsequently  obtained  through  correspondence : 

"Referring  to  the  tank  concerning  which  you  make  en- 
quiry, and  upon  the  preservation  of  which  is  by  some  errone- 
ously attributed  our  existence  as  a  corporation,  I  beg  to  say 
in  reply  to  your  request  for  information,  that  we  are  unable  to 
furnish  any,  as  the  property  upon  which  the  tank  is  situated 
is,  and  has  been,  leased  for  many  years." 

According  to  a  compilation  of  statistics  published  by  '  *  The 
Manual  of  American  Water- works,"  for  1897,  there  are  in 
the  United  States  3215  complete  municipal  water-supply 
plants.  Of  these  2223  are  designed  for  gravity  supply  from 
earth  or  masonry  reservoirs  or  impounding  basins,  small 
wooden  tanks,  or  intended  to  be  operated  entirely  by  direct 
pressure. 

Their  Present  Extent  and  Character. — Nine  hundred  and 
ninety-two  works  are  equipped  with  some  form  of  elevated 
metallic  storage-tanks  or  reservoirs,  approximately  30  per  cent. 
of  the  entire  number  of  plants,  whilst  535>  or  about  50  per 
cent,  of  these  last  have  been  erected  since  1890,  the  figures 
pointing  clearly  along  what  lines  advanced  practice  in  water- 
works design  is  tending. 

The  accompanying  table,  compiled  from  the  *'  Manual  "  for 
'97,  shows  to  what  extent  each  State  has  adopted  metallic 
reservoirs,  their  average  diameter  and  height,  and  a  record  of 
the  material  used  in  the  construction  as  far  as  given.  A  col- 
umn of  low,  or  domestic,  pressure,  and  one  showing  the  fire, 
or  emergency,  pressure  is  also  added.  The  summation  and 
average  of  the  columns  of  figures  given  is  interesting  in  its  in- 
dication of  the  general  practice  and  requirements  deemed 
necessary,  and  from  which  the  composite  stand-pipe  is  20.2 
ft.  in  diameter,  with  a  height  of  62.7  ft.,  capable  of  containing 


ANCIENT  AND    MODERN    WORKS. 


TABLE  No.   i. 

STAND-PIPE    STATISTICS. 


Name. 

Number 

S£ 
J« 
P 

ft 

3f 

'5 
E 

1 

c/5 

c 

0 

ill 

j 

fill 

K 

28 

CQ 

Q 

f.c 

^ 

New  Hampshire... 
Vermont    

8 

27 

00 

66 

•3  q 

2 

05 
63 

Rr» 

99 

86 

Massachusetts  .... 
Rhode   Island 

54 

31 

qO 

69 

7  1 

7 

22 

63 

90 

R/i 

•3Q 

6c. 

4 

75 

04 
Re 

New  York  

7J_ 

2q 

7Q 

TQ 

57 
fie 

°5 

2O 

QC 

1v 

°5 

R<7 

2  1 

8l 

1  J 

51 

Delaware        . 

5U 

12 

88 

4 

7° 

i  R 

Tr.ft 

Maryland     .  . 

4 

16 

oo 

4° 

fir* 

District  Columbia. 

none 

94 

Virginia    

2q 

67 

5 

Tr.£> 

West  Virginia  
North  Carolina.... 
South  Carolina.... 

15 

JO 

8 

35 
20 
16 

49 

100 

96 

80 

3 
5 

2 

2 
2 

4 

91 

95 
47 
43 

127 
lO^ 
114 

A5 

I  Q 

°v 

IOO 

4 

59 

fi-3 

92 

12 

2O 

QC 

°J 

•n 

IJ7 

6 

21 

QC 

7° 

cfi 

Toft 

Louisiana 

I  A 

I  20 

D° 

8 

2O 

1  20 

j 

45 
fii 

Kentucky.  .  .  . 

TO 

2q 

104 

A 

UJ 

fio 

Ohio  

1  J 

21 

IO2 

27 

j  j 

fiA 

inR 

Indiana  

24. 

17 

IOO 

8 

U4 
60 

Michigan    

oq 

21 

8O 

5 

5 

cfi 

yz 

60 

14. 

ToC 

2*7 

5° 

"Wisconsin  

2O 

2O 

IOO 

5^ 
fi/i 

107 

^4. 

14 

80 

17 

°4 

IJ3 

inR 

Minnesota  

12 

^8 

18 

1C 

88 
108 

6 

8 

JO 

bJ 
60 
60 

130 

TTQ 

Nebraska 

46 

T^ 

oo 

IA 

South  Dakota  

16 

QO 

j 

55 
fie. 

North  Dakota 

none 

°5 

I3O 

none 

Montana  

i 

25 

CQ 

fie 

Missouri             .... 

OQ 

14. 

Q7 

5 

fin 

Arkansas  

18 

18 

IO4 

2 

fin 

CQ 

T7 

TQ 

T  rft 

e 

2q 

7q 

j 

51 
62 

New  Mexico  

none 

i 

14 

IOO 

J.^ 

60 

q 

15 

yc 

I 

o« 

Oregon     

none 

*California  

26 

81 

Utah  

none 

°7 

Idaho  

i 

JC 

80 

j 

gc 

Re 

Oklahoma          .    • 

2 

j  i 

127 

2 

fi7 

°5 

.... 

°7 

*  Many  of  wood. 


8  TOWERS  AND    TANKS   FOR    WATER-WORKS. 

150,686  U.  S.  gallons  of  water.  The  average  normal  pressure 
is  found  to  be  62.1  Ibs.  per  sq.  inch  along  the  distributing 
system,  and  this  pressure  is  increased  in  times  of  emergency 
to  104  Ibs. 

The  pressure  62.  I,  under  daily  conditions,  is  equivalent  to 
143.5  ft.  head,  therefore  the  typical  stand-pipe  has  been 
erected  upon  some  convenient  elevation  80.8  ft.  above  the 
general  points  of  distribution.  These  figures  have  a  peculiar 
interest  in  that  the  pressures  determined  represent  those  se- 
cured by  actual  design,  independent,  as  is  frequently  the  case 
with  earth  and  masonry  dams  and  reservoirs,  of  natural  loca- 
tions. It  should  be  remarked  that  the  compilation  includes, 
under  the  head  of  stand-pipes,  only  cylindrical  metallic  struc- 
tures, unsupported  except  by  foundations,  but  all  such  have 
been  incorporated  in  the  summation  and  average,  whether 
intended  for  storage,  regulation,  or  both  combined. 

Eccentricity  of  Design. — In  the  compilation  of  the  fore- 
going table,  the  author  was  much  interested  in  the  special 
features  of  individual  stand-pipes  and  tanks,  where  considerable 
eccentricity  and  lack  of  uniformity  exists,  as  will  be  shown  by 
the  following  two  examples: 

The  tank  of  greatest  capacity  to  this  date  in  the  United 
States  is  that  erected  at  Greenwich,  Conn.,  designed  by  Mr. 
Wm.  S.  Bacot,  C.E.,  and  erected  in  1889  at  a  cost  of  $12,000, 
including  painting  and  foundations.  This  tank  is  of  wrought 
iron,  of  45,000  Ibs.  specified  tensile  strength.  It  is  80  ft. 
in  diameter  by  35  ft.  in  height,  and  is  capable  of  containing 
1,319,472  U.  S  gallons.  The  thickness  of  plates  composing 
the  tank  are  as  follows:  bottom,  T5^  in.  ;  the  1st  ring  is  -J-  in. 
and  the  top  rings  i  in.  iron.  The  joints  are  fastened  with 
butt-straps.  The  structure  is  erected  upon  a  concrete  foun- 
dation, presumably  without  anchorage. 

In  comparison  with  this  colossus,  may  be  cited  a  stand- 
pipe  designed  and  erected  in  1876,  at  Winona,  Minnesota, 


ANCIENT  AND    MODERN    WORKS.  9 

by  Mr.  George  C.  Morgan,  C.E.  This  stand-pipe  is  a  steel 
cylinder,  4  ft.  in  diameter  by  210  ft.  in  height,  capacity 
20,000  gallons.  It  is  enclosed  in  an  outer  ring  of  stone  and 
brick  masonry,  with  a  28-in.  annular  space.  The  lower  50  ft. 
is  composed  of  \  in.  steel  plate;  the  upper  rings  not  stated. 
The  pipe  rests  upon  18  ft.  depth  of  solid  masonry,  and  the 
entire  construction  is  supported  by  timbers  arranged  to  form 
a  platform  24  ft.  square,  resting  upon  a  sub-foundation  of 
water-bearing  sand  and  gravel. 

Of  the  stand-pipes  recorded,  228  are  constructed  of  steel, 
and  195  of  iron,  the  remaining  number  uncertain. 

Besides  the  usual  form  of  stand-pipes  and  tanks,  there  are 
many  towers  and  tanks,  combination  affairs,  designed  to 
meet  certain  conditions  where  it  may  seem  preferable  to  carry 
the  effective  head  of  water  by  open  structural  supports, 
rather  than  by  utilizing  the  lower  plate-rings  of  the  shell  to 
enclose  the  sustaining  water-column.  These  supporting 
towers  are  of  manifold  design  and  construction,  being  built 
sometimes  of  wood,  but  more  frequently  of  stone  or  brick 
masonry,  latterly  largely  of  metal. 

Tendency  of  Modern  Practice. — In  this  connection,  the 
"  Manual"  editorially  says: 

"In  the  design  of  elevated  tanks,  curved  bottoms  have 
recently  been  used  in  a  number  of  instances,  and  steel  sup- 
porting towers  or  trestles  are  now  commonly  employed.  The 
elevated  tank  is  now  preferred  by  many  engineers  to  the 
stand-pipe,  it  being  recognized  that  in  many  instances  the 
effective  upper  20  or  30  ft.  of  water  can  be  supported  more 
cheaply,  and  perhaps  safely,  by  a  trestle  than  by  a  body  of 
water  enclosed  in  a  cylinder.  Where  high  hills  are  available 
for  sites,  and  storage  is  quite  as  important  as  pressure,  stand- 
pipes  have  advantages  of  their  own." 

From  compilations  by  the  writer,  the  number  of  towers 
and  tanks  at  this  time  in  the  United  States,  utilized  by  city 


IO  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

water-plants,  is  161,  generally  constructed  since  1890.  The 
modern  practice  is  to  build  them  largely  of  structural  or  soft 
steel,  and  although  the  procurable  data  is  not  so  full  or  com- 
plete as  the  records  of  stand-pipes  in  the  United  States,  the 
general  average  diameter,  height,  and  capacity  is  as  follows: 
Diameter,  21.3;  height,  36.9;  capacity,  101,100  U.  S.  gal- 
lons, supported  upon  some  form  of  trestle  or  tower  63.5  ft. 
On  account  of  temporary  service  and  liability  to  accident, 
wooden  trestles  are  now  rarely  used  ;  stone  and  brick  masonry, 
although  formerly  much  employed,  has  recently,  on  account 
of  cost,  been  supplanted  by  metallic  towers,  principally  of 
steel. 

Possibly  one  of  the  best  modern  examples  of  the  tendency 
toward  the  erection  of  the  elevated  steel  tower  and  tank  is 
that  lately  constructed  at  Jacksonville,  Florida,  at  a  cost  of 
$10,000,  from  designs  by  Superintendent  R.  M.  Ellis,  C.E., 
1898.  This  tank  is  30  by  45  ft.,  with  conical  bottom  and 
cover,  surrounded  by  an  ornamental  balcony  about  its  base. 
The  tank  is  supported  by  10  6-in.  "  Z"-bar  columns,  100  ft. 
in  height,  stiffened  with  8-in.  "  I  "-beam  ties,  and  the  usual 
diagonal  tie-rods.  The  steel  in  the  columns  is  specified 
to  have  a  tensile  strength  of  70,000  to  75,000  Ibs.  ;  elastic 
limit  40,000  Ibs.,  with  an  elongation  of  20  per  cent,  in  8-in., 
and  a  reduction  at  fracture  of  40  per  cent. 

Steel  for  the  tank,  straps,  rods,  and  rivets  is  to  be  of 
60,000  Ibs.  as  a  maximum  and  56,000  Ibs.  as  a  minimum  ten- 
sile strength  ;  25  per  cent,  elongation  in  8-in.,  and  50  per  centc 
reduction  at  point  of  fracture. 

No  chemical  requirements  have  been  made.  The  joints 
are  made  by  butt-strap,  and  the  usual  requirements  for  shop- 
practice  and  field-work  are  insisted  upon. 

On  account  of  the  importance  of  this  structure  and  its  close 
likeness  to  the  notable  tank  whose  failure  at  Fairhaven,  Mass., 
has  given  rise  to  much  discussion,  and  hereinafter  mentioned 


ANCIENT  AND   MODERN   WORKS. 


II 


.Lattice 


FIG.  i. — TANK  DETAILS  WATER-TOWER  AT  JACKSONVILLE,  FLA, 


12  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

at  considerable  length,  for  the  purpose  of  comparison  and  foi 
general  information,  the  Jacksonville,  Fla.,  water-tower  is  shown 
in  detail. 

Record  of  Failures. — During  the  year  1894,  Prof.  W.  D. 
Pence,  M.  Am.  Soc.  C.  E.,  published  his  monograph,  "Stand- 
pipe  Accidents  and  Failures,"  comprising  a  record  of  such  occur- 
rences from  the  earliest  procurable  data  to  the  time  of  publication, 
and  a  careful  investigation  of  the  facts  from  every  procurable 
source,  systematically  classified  in  convenient  form  and  con- 
cluding with  a  general  discussion  concerning  current  practice 
of  design,  material,  and  construction.  These  studies  are  of 
great  value  and  interest  and  comprise  the  history  of  45  accidents 
to  stand-pipes,  of  which  23  were  total  wrecks,  14  were  slightly 
damaged,  and  8  were  partially  injured.  As  far  as  determined, 
the  cause  of  the  accident  was  in  22  cases  due  to  water;  in  n 
cases  water  and  ice;  n  were  reported  as  due  to  the  wind,  while 
a  number  of  accidents  were  from  failure  of  foundation. 

Of  these  recorded  failures,  7  were  small  wooden  tanks,  19 
were  of  steel,  and  9  of  wrought  iron.  For  a  further  study  of 
these  failures,  their  underlying  causes,  and  the  lesson  taught 
by  each  the  reader  is  referred  to  Prof.  Pence's  admirable  work. 

Believing  that  it  would  be  of  general  interest  that  this  record 
be  brought  up  to  date,  the  following  contains  such  facts  as  the 
author  has  been  able  to  gather  from  many  sources: 

Griswold,  la.,  April  13,  1895. — A  few  hours  after  the  stand- 
pipe  filled  for  the  first  time  it  began  to  settle  to  the  northwest 
and  cracks  opened  between  foundation  and  ground  on  east  side 
and  clay  compressed  on  west  side.  On  emptying  as  soon  as 
possible  the  top  was  found  at  least  13  inches  out  of  plumb.  Foun- 
dation concrete,  about  7  feet  deep,  not  concentric  with  foundation 
and  manhole  vault  of  concrete  extends  6  feet  beyond  standpipe, 
but  is  virtually  part  of  concrete  foundation.  Load  per  square 
foot  3,600  Ibs.  The  pipe  was  continued  in  use.  When  about 
half  full,  leans  12  to  13  inches;  full,  16  inches.  Dimension 


ANCIENT  AND   MODERN   WORKS.  13 

of  tank  10  X  100  feet.  Engineers,  Andrews  £r=  Burnell,  Freemont, 
Neb.  Contractors,  Fremont  Foundry  £r=  Machine  Co.  The 
latter  write  that  there  was  nothing  the  matter  with  the  tank  itself, 
but  that  the  foundations  were  built  over  a  bed  of  quicksand, 
and  after  filling  and  during  a  heavy  gale  of  wind  the  tank  settled 
3  feet  out  of  plumb.  (Engineering  News,  May  13,  1895.)  W.  W. 
Manual,  Fremont  Foundry  £r>  Machine  Co.;  W.  D.  Lovell,  C.E. 

Red  Oak,  la. — Abstract  from  article  in  Engineering  News, 
April  13,  1895:  A  22Xioo-ft.  stand-pipe  built  in  1895,  after 
completion  and  being  filled  was  observed  to  lean  some  30  inches 
from  the  vertical.  Concrete  foundation  about  8  feet  deep;  25-ft. 
diameter  at  base;  2 2 -ft.  top,  upon  clay,  hard  and  uniform  when 
dry,  but  very  soft  when  saturated.  During  construction  clay  was 
thoroughly  water-soaked.  This  stand-pipe  was  not  placed  con- 
centrically on  foundation.  Load  on  clay,  2.6  tons  per  square  foot. 
W.  D.  Lovell,  C.E. 

Lena,  111.,  Dec.  25,  1895. — Uncomplete  masonry  tower  failed 
before  tank  was  placed.  Upper  20  feet  of  one  side  fell.  Prob- 
ably due  to  green  (unseasoned)  limestone  masonry;  rain,  followed 
by  freezing  weather.  (Abstract  Engineering  News,  Jan.  16,  1896.) 
Contractors,  U.  S.  Wind  Engine  &>  Pump  Co.,  Batavia,  111. 
From  the  latter:  "The  tower  was  designed  by  the  U.  S.  Wind 
Engine  &*  Pump  Co.  to  support  a  <>5,ooo-gal.  tank  on  stone 
tower,  giving  elevation  to  bottom  of  tank  of  100  feet  above  the 
water-table. 

"  The  foundation  was  in  heavy,  clay  soil;  an  excavation  was 
made  10  feet  in  depth;  width  of  foundation  at  bottom  6  feet, 
and  at  top  3  feet  6  inches.  The  main  wall  was  carried  up 
from  3  feet  in  width  at  the  water-table  to  18  inches  in  width  at 
the  top.  The  tower  was  about  90  per  cent  completed  when 
the  accident  happened. 

"  The  stonework  was  sublet  to  a  firm  of  contractors,  who  com- 
menced operations  rather  late  in  the  fall,  fifty  feet  of  the  tower 
was  completed  when  freezing  weather  set  in.  The  limestone 


14  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

was  native  rock,  laid  irregularly  in  lo-in.  courses;  the  mortal 
was  composed  of  one-half  cement  and  one-half  lime,  with  a 
fairly  good  quality  of  'Torpedo'  sand,  laid  in  the  usual  pro- 
portions of  hydraulic  cement. 

"  After  50  feet  of  this  work  had  been  completed,  more  or  less, 
cool  weather  was  encountered  during  the  first  few  days  of  Decem- 
ber. About  Dec.  i5th  the  work  was  stopped  pending  a  change 
in  the  weather,  85  feet  of  the  tower  being  then  completed. 

"  On  Dec.  23d  a  sudden  thaw  set  in,  accompanied  by  a  driv- 
ing rain,  which  lasted  all  night.  The  frost  came  out  of  the  stone 
and  mortar  and  the  rain  washed  out  considerable  quantities- 
of  soft  mortar,  and  on  Dec.  24th  a  large  section  of  the  tower 
on  the  south  side  (the  direction  from  which  the  rain  came)  gav^e 
way  extending  down  to  the  5o-ft.  mark. 

11  The  cause  of  the  trouble  was,  in  the  first  place,  due  to  the 
contractor  taking  chances  in  having  continued  cold  weather. 
Had  this  been  the  case  for  a  few  weeks,  the  accident  would  not 
have  occurred. 

"  The  contractor  not  being  financially  responsible,  the  U.  S. 
Wind  Engine  6°  Pump  Co.  tore  down  the  wall  and  built  it  anew 
in  regular  courses,  50  feet  of  stone,  and  the  upper  50  feet  of 
pressed  brick,  and  placed  the  tank  thereon,  since  which  time 
it  has  been  in  satisfactory  working  order  in  every  particular. 

"  The  tower  was  completed  on  the  same  design  so  far  as  the 
proportions  were  concerned,  except  that  we  used  Portland  cement 
in ,  rebuilding.  It  was  also  thought  best  to  continue  the  founda- 
tion work  down  to  the  solid  rock  and  15  feet  farther.  We  do- 
not  think,  however,  that  this  made  any  difference  in  the  safety 
of  the  structure,  as  the  bed  of -clay  was  amply  sufficient  to  support 
superimposed  weight,  as  was  demonstrated  by  examination  of 
the  foundations  when  the  second  excavations  were  made;  it 
showed  no  trace  of  having  settled." 

Garden  City,  Kan.,  April  30,  1896.  During  a  high  wind  a 
loX  i3o-ft.  stand-pipe  (material  not  stated)  failed.  E.  C.  Murphy* 


FIG.  2.— JACKSONVILLE,  FLA.,  WATER-TOWER. 
R.  D.  Wood  6°  Co.,  Philadelphia,  builders. 


(To  face  page  14.)- 


. 


ANCIENT  AND    MODERN    WORKS.  1 5 

hydrographer,  U.  S.  Geological  Survey,  Lawrence,  Kan.,  as~ 
cribed  failure  to  (i)  weak  angle  iron  connecting  bottom  and 
first  course;  (2)  cast-iron  brackets  for  securing  pipe  and  founda- 
tion not  long  and  strong  enough;  (3)  fastening  of  guy-rods  weak. 
The  angle  iron  cracked  four  years  after  construction,  or  about 
1891,  and  four  of  six  brackets  broke  legs.  Brackets  repaired 
with  strap  iron  and  soldered  up.  About  two  and  one-half  years 
before  wreck,  new  section  of  angle  iron  inserted.  At  time  of 
wreck,  crack  appeared  on  north  side  of  angle  iron  and  increased 
in  size  for  one  and  one-quarter  hours,  until  5  feet  long,  with 
water  rapidly  escaping.  Then  angle  iron  (90  feet  from  base), 
to  which  north  guy  was  attached,  gave  way  and  pipe  fell  to  south- 
west. Pipe  was  then  about  one-quarter  full  and  both  pumps 
running.  The  bottom  angle  broke  at  the  angle  all  the  way  round, 
except  where  new  piece  had  been  inserted,  and  here  the  first 
course  of  side  plates  failed  along  the  rivets.  All  cast-iron  brackets 
broke.  (Abstract  Engineering  News,  Oct.  i,  1896.)  As  the  local 
weather  observer  was  not  supplied  with  instruments  for  measuring 
the  intensity  of  the  wind,  its  velocity  at  the  time  of  the  acci- 
dent cannot  be  ascertained.  The  material  used  was  wrought 
iron.  Designing  Engineer,  J.  W.  Uier,  Kansas  City,  Mo.  Con- 
tractors, Palmer  6°  Son,  Kansas  City. 

Cortland,  N.  Y,  Sept.  29,  1896.  Iron  stand-pipe,  f-in. 
plate  at  top  indented  by  wind  about  its  top.  W  nd,  estimated 
velocity  80  miles  an  hour;  22  feet  of  water  in  tank  at  time  of 
accident,  and  extended  2  feet  above  dented  portion  of  tank. 
Size  40X40;  water- works  buil:  in  1884.  There  was  at  the  time 
of  the  accident  no  angle  iron  used  for  stiffening.  After  the 
accident  the  broken  plates  were  removed,  the  bent  portion  pulled 
back  to  shape  with  a  block  and  tackle.  A  patch  replaced  the 
broken  plate,  and  an  angle  iron  was  riveted  inside  of  the  top 
of  the  tank.  Four  steel  guys  were  led  over  the  top  of  the  tank 
to  stone  posts  firmly  set  in  the  ground.  Abstract  of  Engineering 
News,  Nov.  8,  1896.)  Wm.  B.  Landreth,  C.E. 


1 6  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

Atlantic  City,  N.  J.— About  Sept.  12,  1889,  25X132-1^  steel 
stand-pipe  when  partly  full  was  considerably  damaged  by  wind 
blowing  at  an  estimated  velocity  of  100  miles  per  hour.  The 
pipe  was  constructed  in  1883.  In  addition  to  indentation  at 
top,  the  tank  rocked  upon  its  base,  raising  several  inches  on 
the  windward  side.  There  were  no  leaks  and  the  tank  has 
continued  in  service.  (Abstract  Engineering  News,  Nov.  12, 
1896.)  Kenneth  Allen,  C.E.,  Atlantic  City,  N.  J. 

Waco,  Texas,  Oct.  6,  1898. — Stand-pipe,  iron,  20X88,  failed 
when  full  of  water  and  in  service.  According  to  the  superin- 
tendent, the  general  impression  exists  that  the  pipe  was  mali- 
ciously blown  up  by  dynamite.  (Engineering  News,  Oct.  20, 
1898.)  J.  P.  Sample,  Sec.,  Waco,  Texas. 

Fairhaven,  Mass.,  Nov.  9,  1901. — This  elevated  water-tank 
is  particularly  notable  because  the  tank  was  one  of  the  first  with 
a  curved  bottom  ever  erected  in  this  country  and  one  of  the  largest 
of  the  type  built  to  this  time.  The  tank  was  35  feet  in  diameter 
and  50  feet  high,  with  inverted  cone  bottom  for  two  courses,  chang- 
ing to  spherical  form  for  inlet  plate.  Depth  of  cone  about  12  feet. 

The  plate  of  the  tank  at  its  connection  with  circular  girder 
flange  was  J  inch,  the  second  section  was  f  inch,  and  the  inlet 
plate  was  J  inch  thick.  The  tank  was  supported  by  twelve 
inclined  posts  surmounted  by  a  3-ft.  girder,  from  top  of  same  to 
foundations  being  ico  feet.  Dressed-stone  capstones  rested 
upon  rubble  masonry  and  were  secured  by  two  anchor  bolts 
for  each  column.  The  designing  engineer  was  Mr.  Freeman  F. 
Coffin,  and  the  structure  was  built  by  the  Messrs.  Ritter- Connelly 
Mfg.  Co.,  of  Pittsburgh,  Pa.  The  tank-plate  was  originally 
specified  to  be  of  iron,  but  was  subsequently  changed  to  steel, 
which  the  manufacturers  state  was  properly  inspected  and  com- 
plied with  specifications  for  same. 

No  subsequent  tests  of  this  material  were  made  so  far  as 
known,  but  it  is  generally  agreed  that  the  metal  of  the  shell  was 
very  good;  that  of  the  bottom  fairly  good,  with  one  exception; 


ANCIENT  AND    MODERN    WORKS.  \J 

the  butt-straps  were  of  poor    and  brittle  steel,  while  the  tower 
metal  as  far  as  examined  was  of  inferior  quality,  the  fractures 


HO. HEWS  ''*;/V      VltvW> 

FIG.  3. — VIEW  OF  WATER-TANK  AT  FAIRHAVEN,  MASS. 

{Redrawn  from  a  photograph  taken  just  after  the  tank  was  completed.    Practically 
the  same  view  appeared  in  Engineering  News  for  Sept.  5,  1895.) 

being  "as  short  as  they  would  be  in  cast  iron,  and  had  a  granular 
appearance." 

The  temperature  at  the  time  of  the  accident  was  about  freezing, 
with  no  wind. 


1 8  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

Eye-witnesses  state  that  there  was  a  sudden  burst  of  water 
Irom  the  tank,  followed  by  its  immediate  collapse.  When  the 
tank  reached  the  ground  its  conical  bottom  was  almost  wholly 
separated  into  three  parts.  The  cylindrical  portion  of  the  tank 
was  intact  around  the  whole  lower  ring  and  showed  no  signs 
of  failure,  except  for  a  few  openings  in  some  of  the  upper  joints 
caused  by  the  shock  of  falling.  The  bottom  portion  of  six  or 
seven  of  the  supporting  posts  fell  upon  the  top  of  the  tank,  as  did 
also  the  two  lower  lengths,  or  40  feet  in  all,  of  the  lo-in.  wrought- 
iron  feed-pipe.  The  girder  and  parts  which  supported  the  tank 
were  tossed  and  bent  and  buried  underneath  the  tank.  The 
foundations,  except  for  the  displacement  of  two  or  three  of  the 
capstones,  were  unimpaired. 

Wherever  the  bottom  and  the  sides  parted  in  the  wreck,  with 
but  few  exceptions  it  was  the  rivets  that  failed.  An  examination 
of  the  whole  circumference  of  the  angle  iron  attached  to  the 
lower  edge  of  the  sides  of  the  tank  showed  only  three  stretches, 
ij,  ij,  and  8  feet  respectively,  where  the  flange  of  the  bottom 
plates  had  ruptured  and  was  still  attached  to  the  angle  which 
united  the  sides  and  bottom  of  the  tank. 

From  investigation  it  was  found  that  three- fourths  of  the 
failure  was  due  to  rivets  and  but  one-fourth  to  ruptured  plate 
of  the  bottom. 

The  flanged  part  of  the  bottom  plate  was  weakened  by  the 
counter- sinking  for  the  rivets,  yet  where  the  flanged  plate  tore, 
the  rupture  was  along  the  line  of  the  rivet-holes  for  only  two 
stretches  of  six  rivets  each.  The  rivets,  so  far  as  they  remained 
in  evidence,  failed  in  their  lower  or  counter- sunk  heads;  most 
of  these  heads  pulled  right  through  the  bottom  plate,  the  edges 
of  the  counter-sunk  heads  pulling  over  the  end.  None  could 
be  found  which  had  sheared  off.  From  the  original  design  of 
this  tank,  departure  was  as  follows:  (i)  Substitution  of  steel  for 
wrought  iron  in  tank  and  tension  members  of  tower.  (2)  The 
flanged  bottom  of  tank  was  riveted  to  the  angle  only,  instead 


ANCIENT  AND   MODERN    WORKS.  19 

of  being  riveted  to  the  top  of  the  girder  on  both  sides  of  the  web. 
(3)  The  girder  was  changed  from  a  continuous  web  for  the  whole 
circumference  to  construction  in  segments;    riveted  together  at 
the  ends  by  means  of  vertical  angles.     (4)  The  tank  was  anchored 
to  the  tower  by  eye-rods.     (5)  The  butt-straps  covering  the  radial 
joints  were  placed  on  the  outside  instead  of  on  the  inside  of  the 
tank  bottom.     The  initial  rupture  was  assumed  as  having  taken 
place  at  the  juncture  between  the  spherical-shaped  plate  and 
the  inner  ring  of  plates  connected  .with  it.     In  opposition  to  this 
theory,  reference  is  made  to  a  full  discussion  by  Prof.  Marsden, 
p.   179.     The  designing  engineer  offers  the  following  explana- 
tion of  the  disaster:   The  failure  to  rivet  the  bottom  angle  securely 
to  the  head  of  the  girder  as  well  as  to  the  side  angle.    A  movement 
was  caused  by  the  pressure  of  the  water  normal  to  the  bottom, 
which  movement  brought  an  outward  pressure  upon  this  girder, 
which  was  unsupported  except  by  tensile  strength  in  itself.     That 
is  to  say,  there  was  an  outward  pressure  on  this  girder  similar 
to  the  pressure  of  the  side  walls  of  the  stand-pipe  and  possibly 
to  as  great  a  degree.     This  pressure  would,  of  course,  as  in  the 
walls  of  the  stand-pipe,  be  concentrated  at  a  weak  joint,  sufficient 
finally  to  overcome  the  comparatively  small  resistance  of  one 
of  the  joints  where  the  girder  was  riveted  together.     This  joint 
failed  and  the  girder  was  pushed  out,  or  moved  from  under  the 
bottom  at  that  point,  and  the  weight  of  the  water  forced  the 
bottom  away  from  the  angle  iron  by  pulling  the  counter- sunk 
rivets  through  the  plate.     At  the  same  time,  the  whole  tower 
being  weakened  at  the  top,  took  a  twisting  motion;    the  bottom 
plate  fell  down  and  tore  off  the  centre,  and  the  entire  structure 
collapsed.     It  was  believed  by  the  designer  that  the  initial  rupture 
occurred  at  the  sides  and  not  in  the  centre,  as  it  seemed  incredible 
that  the  centre  plate,  even  of  poor  material,  could  have  failed, 
as  the  pressure  at  that  point  was  a  minimum  and  the  thickness 
of  the  material  was  ample  for  the  calculated  stress.     (Abstract 


20 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 


Engineering  News,  Nov.  2ist.)     Freeman  F.  Coffin,  C.E.,  Ritter- 
Connelly  Mfg.  Co. 

Elgin,  111.— The  30X95-^.  stand-pipe  belonging  to  the  City 


si 


Water  System,  constructed  in  1887-88,  burst  on  March  14,  1900. 
Its  capacity  was   502,300  gals,   and  the  foundation  of  the 


ANCIENT  AND    MODERN    WORKS. 


21 


tank  was  20  feet  high,  consisting  of  concrete,  faced  with  brick 
masonry. 

About  6  A.M.  of  the  day  of  the  accident,  the  stand-pipe  having 


FIG.  5. — VIEW  or  STAND-PIPE  AT  ELGIN,  ILL.,  LOOKING  NORTHWEST. 
(Engineering  News.) 

been  pumped  full   the  engines  were  stopped  until  8  A.M.,  when 
the  failure  occurred,  during  which  time  the  water  consumption 


22  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

was  estimated  to  have  withdrawn  the  water  some  20  feet  below 
the  top  of  the  tank. 

The  accident  was  preceded  by  a  crashing  sound  due  to 
falling  ice,  followed  by  a  loud,  rending  report  and  the  rush  of 
water  and  ice  on  the  east  side,  and  ending  in  a  rumbling  sound 
as  the  main  upper  section,  containing  several  hundred  tons  of  ice, 
struck  the  ground.  About  one-fifth  of  the  plates,  consisting  of 
most  of  the  four  lower  rings,  were  torn  loose  from  the  upper  section 
and  from  the  bed-plate,  and  were  projected  by  the  reaction  of  the 
escaping  water  to  the  southeast  of  the  foundation,  while  the 
upper  75  feet  toppled  to  the  east  or  northeast,  falling  vertically 
to  the  foundations,  and  landing,  a  flattened  mass,  in  a  north- 
easterly direction  and  free  from  the  foundation.  An  examination 
of  the  ruins  indicated  that  the  initial  rupture  occurred  on  the 
east  or  northeast  side,  about  four  courses  from  the  base.  The 
holding-down  bolts,  twenty- two  in  number,  failed  mostly  in  the  eye. 

Twice  each  year  since  the  stand-pipe  was  built  it  had  been 
emptied  and  its  interior  carefully  examined.  The  last  inspection 
was  during  the  previous  October,  when  the  stand-pipe  was  said 
to  have  been  in  satisfactory  condition. 

No  leaking  had  been  reported  for  at  least  ten  years,  but  the 
pitting  action  of  the  water  was  quite  marked,  perhaps  not  more 
so  than  is  usual  elsewhere  under  like  conditions.  The  interior 
had  been  repainted  twice  since  the  scand-pipe  was  built,  but 
very  little  of  the  interior  paint  had  survived  the  first  winter  owing 
to  -the  friction  of  the  ice.  The  mean  temperature  from  December 
to  March  for  six  previous  years  was  21.8°. 

For  several  days  preceding  the  accident  the  sun  had  been 
shining  more  or  less,  and  there  was  doubtless  some  thawing 
of  the  ice  in  the  stand-pipe. 

It  turned  cold  the  evening  before  the  failure  and  a  film  of 
ice  \  inch  or  more  thick  formed  against  the  inside  of  the  plates. 

From  a  study  of  ice  fragments,  a  great  tube  of  ice  commonly 
formed  in  exposed  stand-pipes  against  the  metal  shell  had  in 


• 

A  NCI  EN  7^  AND    MODERN    WORKS.  2$ 

4* 

the  Elgin  pipe  a  thickness  of  6  inches  or  so  near  the  bottom  and 
30  inches  or  more  in  the  upper  section  within  30  to  35  feet  range 
of  daily  fluctuation  of  water-line.  It  is  commonly  the  case  that 
the  inlet  of  warm  water  melts  away  and  prevents  the  formation 
of  ice  shell  some  distance  from  the  base  of  stand-pipes,  the  extent 
of  this  action  depending  chiefly  upon  the  temperature  of  the 
water  in  the  mains.  Since  this  had  been  noted  as  about  32° 
previous  to  the  accident,  this  process  of  melting  the  ice  must 
have  been  very  slight  in  the  Elgin  pipe.  Under  these  conditions 
the  circulation  of  water  by  convection  must  have  been  insignificant. 
The  increase  in  thickness  of  the  ice  walls  from  the  base 
upward  was  manifestly  due  to  the  increased  exposure  toward 
the  top.  The  ice  was  originally  moulded  close  against  the  plates 
and  rivets.  It  was  evident,  however,  that  a  film  of  water  had 
formed  between  the  ice  and  metal  shell,  probably  by  action  of 
the  sun  and  warm  winds,  for  some  days  before  the  accident, 
for  the  impressions  of  the  rivet  heads  and  joints,  while  perfectly 
distinct,  were  not  sharply  defined.  This  initial  thaw  is  further 
evidenced  by  the  thin  layer  of  fresh  ice,  which  clung  with  surpris- 
ing adhesion  to  the  inner  surface  of  the  plates  of  the  top  section 
notwithstanding  its  tremendous  impact  with  the  frozen  ground. 
Although  the  J-in.  film  of  new  ice  held  thus  tenaciously  to  the 
metal  sheets,  no  connection  could  be  traced  between  the  fresh 
film  and  the  fragments  of  the  older  ice.  A  careful  examination 
showed  the  top  of  the  ice  mass  in  the  upper  section  just  even 
with  the  upper  edge  of  the  top  ring  of  the  plates  and  the  imprints 
of  the  rivet-heads  in  the  ice  near  the  top  continuously  matching 
the  rivets  themselves,  showing  that  the  ice  tube  had  not  shifted 
longitudinally  in  the  metal  shell.  Since  the  ice-level  was  below 
the  point  of  buoyancy,  it  is  certain  that  the  ice  mass  was  supported 
top  to  top  with  the  stand-pipe  either  by  the  continuity  of  the 
ice  shell  to  the  bed-plate,  or  by  a  frozen  connection  between 
the  ice  and  the  plates,  or  perhaps  both.  In  any  event,  it  seemed 
absolutely  certain  that  the  main  bulk  of  the  ice  moulded  more 


24  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

or  less  closely  against  the  stand-pipe  plates  and  did  not  fall  pre- 
vious to  the  initial  rupture  near  the  base. 

Among  the  countless  fragments  of  ice  were  a  number  of  very 
large  sheets  or  chunks,  two  of  which  fell  upon  the  bed-plate 
and  another  immediately  in  front  of  the  gate-chamber  door. 
These  masses  and  other  boulder-like  pieces  of  almost  spherical 
form  had  unquestionably  floated  on  the  top  surface  of  the  water 
inside  the  ice  tube,  forming  a  broken  sheet  30  inches  to  3  feet 
in  thickness.  With  these  masses  floating  at  or  near  the  top  of 
the  stand-pipe,  with  the  water  surface  held  about  stationary  for 
a  short  time  during  the  previous  night,  a  very  slight  formation 
of  ice,  even  less  than  that  found  on  the  plates,  would  weld  them 
into  a  self-supporting  sheet.  The  failure  of  this  ice  roof  with 
the  falling  water-level  and  consequent  atmospheic  pressure  from 
above,  accompanied  by  the  morning  rise  of  temperature,  would 
account  for  the  crashing  sound  within  the  stand-pipe  heard 
the  instant  before  the  initial  rupture  occurred.  The  capacity 
of  the  stand-pipe  free  from  ice  being  about  500,000  gals,  the 
estimated  volume  of  ice,  assuming  a  shell  95  feet  high,  with  18- 
inch  average  walls  and  a  3o-in.  top  sheet,  was  14,190  cubic  feet, 
which  would  reduce  the  capacity  of  the  full  tank  to  about  400,000 
gals.  With  the  water-level,  say,  at  72  feet  above  the  base,  the 
volume  of  water  in  the  pipe  when  the  failure  occurred  was  not 
far  from  300,000  gals,  from  6  A.M.  to  8  A.M.,  indicating  a  con- 
sumption of  perhaps  100,000  gals,  or  less  during  the  two  hours. 
The  total  weight  of  ice  in  the  stand-pipe,  assuming  these  condi- 
tions, was  about  400  tons,  of  which  35  tons  was  in  the  top  sheet, 
whose  fall  is  supposed  to  have  preceded  the  failure. 

An  examination  of  the  material  of  which  the  pipe  was  com- 
posed showed  considerable  irregularity,  many  fractures  showing 
more  or  less  dead  and  laminated  appearance  and  evidence  of 
brittleness,  such  as  cracks  and  crystalline  spots  in  the  fractures. 
Rivet  fractures  generally  exhibited  satisfactory  material,  although 
the  laying  out  showed  poorly  matched  holes ;  there  were  also  signs 


9 
ANCIENT  AND    MODERN    WORKS.  2$ 

of  cracks  about  the  rivet-holes,  indicating  damage  in  punching 
brittle  plate.  Physical  tests  of  samples  of  the  plate  were  made 
at  Purdue  University,  as  was  also  a  test  to  determine  percentage 
of  phosphorus,  with  the  following  results: 

Original  area  in  sq.  ins 5625  -5754 

Elongation  in  8,  in  per  cent 22.5  23.5 

Reduction  of  area,  per  cent 47-7  4°-5 

Elastic  limit,  per  sq.  in.,  Ibs 37,020 

Ultimate  strength  per  sq.  in.,  Ibs 58,490  55>96o 

Character  of  fracture,  coarse,  silky;  laminated. 

The  test  for  phosphorus  was  made  upon  a  sample  which  ap- 
peared unusually  brittle  and  had  an  especially  poor  fracture. 
The  analysis  showed  .091%  phosphorus. 

Examining  the  list  of  plate  thickness,  it  appears  that  the 
Elgin  stand-pipe  was  designed  with  a  safety  factor  of  4,  assuming 
70%  joint  efficiency  with  6o,ooo-lb.  steel  plate.  The  spacing 
and  diameter  of  rivets  as  found  in  the  lower  rings  was  not  such 
as  to  give  the  assumed  70%  efficiency.  In  the  fourth  ring  the 
rivets  had  a  pitch  of  about  i\  ins.  with  i-in.  rivet-holes,  which 
would  reduce  the  efficiency  of  the  joints  to  60%  and  increase 
the  working  stress  with  a  full  tank  from  15,000  to  17,500  Ibs. 
per  square  inch  in  the  net  section.  With  the  water  at  the  72-ft. 
level  at  the  time  of  the  accident  the  stress  due  to  hydrostatic 
pressure  alone  was  perhaps  13,000  Ibs.  per  square  inch  in  the 
rings  near  the  base,  where  the  failure  occurred.  The  quite  general 
practice  of  using  a  safety  factor  of  4  in  stand-pipe  design  has 
doubtless  been  based  upon  the  assumption  of  quiescence  in 
the  loading,  as  in  building  construction.  In  the  case  of  a  stand- 
pipe  properly  encased  from  the  action  of  the  ice  and  wind 
this  assumption  is  doubtless  consistent,  although  the  prevailing 
practice  in  good  bridgework  of  using  low  working  stresses  for 
loads  frequently  applied  might  warrant  the  use,  even  in  the 
protected  stand-pipe,  of  safer  unit  loads  than  those  obtained 
with  a  factor  of  4.  In  any  event,  the  Elgin  stand-pipe  is  open 


26  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

to  severe  criticism  in  that  its  metal  has  probably  been  subjected 
to  as  much  as  17,500  Ibs.  per  square  inch  under  daily  service, 
which  represents  a  factor  of  safety  of  less  than  3.5  as  compared 
with  the  ultimate  strength  of  60,000  Ibs.;  or  if  compared  with 
the  elastic  strength  of  say  30,000  Ibs.  per  square  inch,  a  "co- 
efficient of  security"  of  1.7  or  so.  The  latter  is  the  more  correct 
basis  of  judgment  of  the  safety  of  a  stand-pipe,  since  total  failure 
is  almost  certain  to  follow  the  opening  up  of  the  rivet-holes, 
about  which  cracks  or  defects  are  most  likely  to  occur. 

The  Elgin  stand-pipe  is,  of  course,  open  to  the  sweeping 
criticism  which  may  be  directed  against  the  large  number  of 
stand-pipes  which  have  no  protection  from  the  elements,  espe- 
cially those  in  icy  latitudes.  If,  as  must  be  conceded,  intelligent 
design  provides  against  a  dangerous  condition,  which  is  certain 
to  exist,  then  the  Elgin  stand-pipe  was  defective  in  design  in 
that  ice  could  form  within  it  in  dangerous  quantities.  Beside 
the  fall  of  the  ice,  other  possible  dangers  from  the  action  of  ice 
have  been  taken  into  consideration.  One  of  these  is  the  increased 
rivet  shear  due  to  the  possible  suspension  of  800,000  Ibs.  of  ice 
from  the  top  rim,  which  would  amount  to  about  1800  Ibs.  per 
rivet.  Still  another  danger  was  in  the  formation  of  the  ice-cap 
by  which  the  rivet  shear  might  be  very  greatly  increased  from  the 
atmospheric  pressure  as  the  water  was  drawn  off,  or  the  stand- 
pipe  might  be  overstrained  by  the  sudden  starting  of  the  pumps. 
Should  a  perfect  vacuum  form  beneath  the  ice-cap,  the  increased 
vertical  shear  would  be  about  3300  Ibs.  per  rivet,  which,  added 
to  that  due  to  the  suspended  ice,  would  produce  a  rivet  shear 
of  say  5000  Ibs.  per  rivet  above  that  considered  in  the  design. 
Still  another  danger  from  ice  is  suggested  by  the  existence  of 
the  water  film  due  to  thaw  against  the  plates.  In  case  the  ice 
shell  had  a  water-tight  connection  with  the  bed-plate,  as  might 
appear  possible  from  the  low  temperature  of  the  supply,  and 
be  free  from  cracks  so  as  to  isolate  the  film  from  the  main  body 
of  water,  the  dangers  would  be  much  the  same  as  those  which 


ANCIENT  AND    MODERN    WORKS.  2*J 

caused  the  failures  at  Asheville,  N.  C.,  and  Providence,  R.  I. 
These  conditions  are  not  unlike  those  which  sometimes  occur 
in  a  refrigerating-plant  when  a  breakdown  for  a  few  hours  may 
allow  a  film  of  water  to  thaw  between  the  ice  mass  and  the  sides 
of  the  freezing-can.  Under  such  circumstances  the  sides  of  the 
cans  are  sometimes  seriously  bulged  when  the  refrigeration  is 
resumed.  These  various  possible  or  probable  dangers  from  ice 
action  merely  go  »to  enforce  the  importance  of  so  encasing  stand- 
pipes  as  to  prevent  the  formation  of  ice  within  them.  The 
opinion  of  Prof.  W.  D.  Pence,  who  reported  the  accident  for  the 


FIG.  6. — GENERAL  VIEW  OF  RUINS  or  THE  ELGIN  STAND-PIPE.     (Eng.  News-) 

Engineering  News,  an  abstract  of  which  is  here  given,  is  that 
the  'accident  was  probably  due  to  the  following  causes : 

"(i)  That  the  specifications  for  the  Elgin  stand-pipe  were 
faulty  in  the  tests  for  plate  metal,  and  that  improper  material 
was  used. 

"  (2)  That  the  working  strains  in  the  plate  metal  were  exces- 
sive. 

"  (3)  That  the  failure  would  probably  have  occurred  even 


28 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 


with  first-class  material,  owing  to  the  exposure  of  the  structure 
to  the  elements  in  the  icy  latitude. 

"  (4)  That  the  primary  cause  of  the  accident  was  the  fall  of 


FIG.  7. — VIEW  SHOWING  EFFECT  OF  WIND  ON  STAND-PIPE  AT  LINCOLN,  NEB. 
(Engineering  News.) 

ice,  due  to  the  improper  control  of  the  water-level  during  the 
critical  ice  period." 
/        Lincoln,   Neb. — On  April  22,  1902,  a  25X100- ft.  stand-pipe, 


ANCIENT  AND    MODERN    WORKS.  29 

constructed  of  steel,  was  badly  damaged  by  the  wind  with  a 
recorded  velocity  of  from  33  to  60  miles  an  hour,  with  an  average 
for  five  minutes  of  57  miles.  The  pipe  was  located  upon  a  hill, 
and  the  wind  had  full  sweep  against  it  from  every  side.  The 
stand-pipe  was  erected  upon  a  concrete  foundation  of  ample 
strength,  and  upon  which  it  was  observed  to  rock  back  and 
forth  during  the  storm,  breaking  two  anchor  rods  on  the  south 
side,  showing  a  crystalline  fracture.  All  of  the  rods  were  found 
with  their  nuts  off  of  their  heavy  batter  washers. 

The    specifications    called    for   the    following    thickness    and 
weights  of  plate. 

Section,  ft.  from  bottom.  Thickness,  in.     Weight  per  sq.  ft.,  Ibs. 

Bottom  plate 1/2  20.0 

i  to      5ft 3/4  30.0 

6  '      10  " ii /i 6  28.0 

21  '      30  " 5/8  25.0 

31*      4°  " 9/16  22.5 

41'      45" 7/16  I7-S 

46'      55  " 3/8  15-0 

56'      65  " 5/i6  12.5 

66  '      80  " 1/4  10. o 

81  '    ioo  " 3/i6  7.5 


The  other  chief  features  of  the  specifications  were:  T.  S., 
60,000  Ibs.  per  square  inch.  Vertical  seams,  D.  R.,  and  horizontal 
seams,  S.  R.  Bottom  united  to  shell  by  6  in.X6  in.  steel  angle; 
top  stiffening  ring  to  be  3^X3^  steel  angle  securely  riveted  to 
plate.  Eight  anchor- rods,  1}  inches  diameter,  securely  anchored 
in  concrete  foundations  and  passing  through  heavy  lugs  riveted 
to  shell.  Plates  to  be  such  size  that  eight  plates  make  a  course 
of  25  feet  diameter  and  twenty  courses  a  height  of  ioo  feet. 

The  angle  stiffening  ring  was  broken  in  several  places.  This 
ring  was  in  sections  riveted  on  the  outside  of  the  shell.  The 
joints  were  butt-joints  held  by  flat  plates.  The  exact  amount 
of  water  in  the  tank  during  the  storm's  greatest  intensity  was 


30  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

uncertain,  but  was  supposed  to  approximate  60  feet.     (Engineer- 
ing News,  May  15,   1902.) 

Normandy  Heights,  near  Baltimore,  Md. — During  the  latter 
part  of  December,  1901,  a  steel  stand-pipe  25X60  feet,  belong- 
ing to  the  Roland  Parl  Co.,  partially  failed.  The  structure  was 
erected  upon  a  foundation  of  stone  7  feet  high.  The  stand- 
pipe  was  constructed  in  5 -ft.  rings,  with  thickness  as  follows : 
First  ring,  J  inch;  3  rings,  7/16;  4  rings,  f;  and  4  rings  5/16 
inch.  At  a  point  52  feet  6  inches  above  the  foundations  there 
was  a  division  in  the  tank,  forming  a  high-service  reservoir  7 
feet  6  inches  deep.  The  water  main  supplying  the  tower  entered 
at  the  foundation  and  extended  through  the  lower  section,  dis- 
charging into  the  high-sendee  compartment.  Beginning  near 
the  bottom  of  this  compartment,  another  pipe  was  carried  to  a 
point  near  the  top  of  the  structure,  providing  an  overflow  into 
the  low-service  compartment  after  the  high-service  tank  had 
been  filled.  There  are  few  water  consumers,  and  the  tank  was 
not  pumped  into  except  at  intervals  of  four  or  five  days,  thus 
facilitating  the  process  of  freezing  during  suitable  weather  such 
as  had  existed  prior  to  the  failure.  Ice  had  formed  to  considerable 
thickness  over  the  surface  of  the  water  in  both  sections  of  the 
tank.  The  inlet  pipe  was  probably  also  frozen  at  some  point 
in  its  length,  for  when  the  water  was  turned  on  the  attendant 
found  that  the  pipe  seemed  to  be  stopped  up  and  proceeded 
to  open  a  man-hole  at  the  bottom  of  the  tank  to  draw  off  the 
water,  intending  to  build  a  fire  in  the  lower  section  to  thaw  the 
pipe.  He  states  that  a  heavy  mass  of  ice,  formed  at  the  partition, 
fell,  bending  in  the  braces  that  supported  that  partition  and 
high-service  compartment,  and  thus  drew  the  plate  in,  bending 
the  sheet  on  one  side  down  nearly  to  the  middle  of  the  stand-pipe. 
It  was  suggested  that  the  vacuum  produced  by  drawing  off  the 
water  was  the  cause  of  the  trouble,  but  this  theory  is  hardly 
tenable,  and  the  attendant's  idea  as  to  the  cause  of  the  failure 
is  more  likely  correct.  Kenneth  Allen,  Engineer  and  Superin- 


f 

ANCIENT  AND    MODERN    WORKS.  31 

tendent,  Atlantic  City,  N.  J.;  Richard  W.  Marchant,  Jr.,  Balti- 
more. 

A  water  tower  at  Abeline,  Texas,  consisting  of  a  steel  tower 
70  ft.  high,  surmounted  by  a  steel  tank  25  ft.  in  diameter  by  20 
ft.  in  height,  collapsed  immediately  after  completion  (April,  1904), 
an  account  of  which  is  as  follows: 

"  When  the  structure  was  completed,  except  painting  and 
riveting  of  a  balcony  floor,  water  was  pumped  into  the  tank. 
From  the  time  spent  in  pumping  there  was  supposed  to  have 
been  from  16  to  17  ft.  of  water  in  the  tank,  when  the  entire 
structure  collapsed,  falling  within  its  own  foundations  a::d 
making  a  complete  wreck. 

"The  examination  of  the  wreckage  pointed  to  the  weakness 
of  the  framework,  as  the  tank  came  down  in  one  piece,  with 
the  bottom  split  full  length,  caused,  the  writer  believes,  from 
its  contact  with  the  earth,  as  it  appears  to  have  struck  on  its 
side.  No  one  witnessed  the  fall  its  entire  length.  Two  young 
men  were  standing  near  the  tower  when  they  heard  a  crack,  as 
they  explained,  like  the  report  of  a  rifle,  and  they  turned  and 
fled." 

This  completes  the  list  of  all  failures  of  metal  water-towers 
and  tanks  to  date,  although  a  feature  of  the  past  two  years  has 
been  the  many  failures  of  elevated  wooden  tanks,  the  great  per- 
centage of  which  failed  by  the  rusting  out  and  subsequent  rupture 
of  the  flat  encircling  hoops.  To  such  an  extent  has  this  cause 
resulted  in  the  complete  collapse  of  such  structures,  that  under- 
writing agencies,  who  have  in  many  instances  specified  such 
structures  for  fire  protection,  are  now  insisting  that  all  hoops 
shall  be  made  of  round  rods  instead  of  the  flat  bands  heretofore 
largely  used. 

Of  the  later  failures,  it  will  be  noted  that  3  were  due  to  defec- 
tive foundations;  4  failed  during  heavy  gales;  2  were  damaged 
by  ice  formation,  and  i  was  wrecked  simply  by  hydrostatic 
pressure. 


TOWERS  AND  TANKS  FOR  WATER  WORKS. 


bo 
I 


ANCIENT   AND  MODERN  WORK. 


31* 


Of  the  total  failures  due  to  wind,  ice,  and  water,  2  were  tanks 
constructed  of  wrought  iron  and  4  of  structural  steel. 

After  examination,  several  engineers  reported  that  beside 


FIG.  i. — View  of  Wrecked  Water  Tank-tower  at  Abilene,  Texas. 

faulty  details  of  a  faulty  character,  the  weakness  of  the  main 
members,  particularly  of  the  floor,  was  amply  sufficient  to 
account  for  the  accident. 


CHAPTER   II. 

THE    CHEMICAL   AND   PHYSICAL    PROPERTIES    OF 
STRUCTURAL   METAL. 

Wrought  Iron. — In  attempting  to  discuss  the  physical  and 
chemical  properties  of  the  structural  metals,  investigation 
leads  by  many  stages  from  geological  and  metallurgical  con- 
ditions existing  in  Nature's  great  laboratory  to  those  finished 
products  daily  used  in  the  mechanical  arts.  Each  step  in  this 
process  of  evolution  has  been  given  the  devoted  attention  and 
wisdom  of  learned  scientists,  who  have  contributed  to  the  world 
the  results  of  their  researches  in  many  erudite  and  volumi- 
nous works.  It  is  not  within  the  scope  of  this  volume  to  do 
more  than  attempt  to  explain  certain  pertinent  features  of 
this  complex  subject. 

In  general  metallic  reservoirs  and  their  supports  are  con- 
structed of  riveted  plates  and  members  of  iron  or  steel. 
Until  the  last  decade  iron  was  almost  universally  employed, 
but  improved  processes  of  manufacture,  reducing  at  the  same 
time  the  cost  of  the  product  and  eliminating  the  uncertainty 
of  the  result,  has  produced  a  radical  change  in  this  practice, 
until  steel  has  attained  first  place  as  a  suitable  metal  for  struc- 
tural purposes. 

In  the  production  of  wrought  iron,  the  chemical  process 
is  the  conversion  of  crude  or  ''pig"  iron  into  a  refined  or 
"  merchantable  "  product  by  recarburization  in  a  "puddling 
furnace."  For  the  manufacture  of  wrought  iron,  the  lower 
grades  of  smelted  or  "pig"  iron  are  employed.  The  mechan- 
ical process  of  "  puddling  "  is  melting  and  stirring  the  pig  iron, 

32 


PROPERTIES  OF  STRUCTURAL  METALS.  33 

until  the  proper  degree  of  oxidation  is  secured,  and  then 
working  of  the  molten  metal  into  a  pasty  mass  or  "puddle- 
ball,"  which  may  then  be  squeezed  or  hammered  into  a  suit- 
able shape  or  "bloom"  for  rolling  into  bars,  technically 
known  as  "muck-"  or  "puddle-bars."  When  cold,  this  inter- 
mediate product  is  sheared  and  bundled  into  piles  of  proper 
sectional  area,  to  which  wrought  scrap  is  most  commonly 
added,  after  which  the  pile  so  formed  is  brought  to  a  welding 
heat  in  a  "heating-furnace,"  to  be  afterward  passed  through 
the  finishing  rolls,  becoming  "merchant  iron,"  a  finished 
product. 

The  strength  and  quality  of  the  finished  product  depends, 
naturally,  upon  the  character  of  the  crude  iron  or  "stock," 
the  skill  in  puddling,  or  reducing  the  non-metallic  sub- 
stances, and  particularly  upon  the  method  and  materials  used 
in  forming  the  "pile"  to  be  made  into  "blooms."  All  met- 
allic iron  contains  more  or  less  impurities,  and  in  general  such 
elements  as  silicon,  manganese,  carbon,  sulphur,  and  phos- 
phorus appear;  the  best  wrought  iron  can  only  be  produced 
from  crude  iron  containing  a  limited  percentage  of  sulphur 
and  phosphorus,  neither  of  which  can  be  entirely  eliminated 
in  the  puddling  process,  a  sufficient  percentage  being  left  in 
the  product  to  give  unfavorable  results  if  they  were  able  to 
exert  their  full  effect  in  the  production  of  crystallization  of 
the  fibres  of  the  metallic  iron ;  but  the  slag,  resulting  from  the 
other  non-metallic  impurities,  overcomes  this  tendency  in  a 
degree. 

The  presence  of  considerable  percentages  of  sulphur  pro- 
duces in  the  finished  iron  a  condition  termed  by  smiths  as 
"  red  short  " — an  inclination  to  disintegrate  or  crumble  when- 
ever the  iron  is  heated  to  a  working  temperature  ;  the  cohesion 
of  its  particles  being  affected  adversely,  the  strength  of  the 
metal  is  correspondingly  reduced. 

The  effect  of  phosphorus,  the  most  detrimental  of  all  the 


34  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

alloys,  is  exactly  opposite  to  that  produced  by  excess  quanti- 
ties of  sulphur,  in  that  it  makes  the  finished  product  ''cold 
short,"  crystalline  in  appearance,  of  uncertain  strength,  and 
liable  to  fracture  from  sudden  shock. 

That  the  character  or  arrangement  of  the  piles  has  a  direct 
relation  to  the  strength  of  the  product  is  explained  by  Camp- 
bell as  follows:  "If  the  piles  were  square  and  were  made  up 
of  similar  pieces  of  equal  length,  each  layer  being  at  right 
angles  to  the  one  below,  and  if  the  bloom  were  rolled  equally 
in  each  direction,  it  is  evident  that  the  plate  would  be  as 
strong  in  the  line  of  its  length  as  of  its  breadth ;  but  as  the 
bars  from  which  the  pile  is  formed  have  been  made  by  stretch- 
ing the  material  in  one  way,  and  as  all  practical  work  requires 
a  piece  of  greater  length  than  width,  it  will  be  seen  that  the 
finished  product  will  show  much  better  results  when  tested  in 
the  direction  of  its  length  than  its  width.  The  result  will 
also  depend  upon  the  skill  with  which  the  pile  has  been  con- 
structed ;  upon  the  perfection  of  the  welding  as  influenced  by 
the  heating  and  the  rapidity  of  handling,  and  upon  the  free- 
dom of  the  iron  from  thick  layers  of  slag." 

To  secure  a  pure,  refined  iron,  such  as  should  be  specified 
for  structural  work,  it  is  necessary,  first,  to  require  that  the 
chemical  components  of  the  crude  iron  shall  be  such  as 
under  favorable  treatment  shall  give  the  desired  chemical 
product;  secondly,  the  production  of  the  muck-bar  in  suitable 
condition  being  largely  dependent  upon  the  skill  of  the  work- 
men, other  things  being  equal,  preference  should  be  given  the 
product  of  old  and  reputable  establishments,  and  this  applies 
with  equal  force  to  the  finished  product,  for  it  is  customary  in 
the  manufacture  of  finished  iron  to  utilize  large  quantities  of 
miscellaneous  "  scrap  iron/'  purchased  in  the  open  market, 
and  this  scrap,  without  any  careful  or  intelligent  assortment, 
is  piled  with  the  sheared  muck-bar  until  the  proper  size  and 
weight  bloom  are  obtained,  when  it  is  heated  to  a  welding 


PROPERTIES   OF  STRUCTURAL   METALS.  35 

heat  and  rolled  into  the  required  shape.  The  effect  of  scrap 
steel  or  of  impure  metal  within  the  mass  of  this  pile  is  to  de- 
stroy the  homogeneity  and  produce  segregation. 

Whilst  it  is  true  that  sometimes  carelessness  is  responsible 
for  such  process  of  manufacture,  more  frequently  it  is  the  di- 
rect result  of  determined  effort  upon  the  part  of  the  manufac- 
turer to  cheapen  his  product  by  utilizing  cheap,  miscellaneous 
scrap  metal.  When  nicked  and  broken  across,  or  when  rup- 
tured under  tension,  the  appearance  of  this  iron,  instead  of 
the  long,  fibrous  arrangement  of  the  molecules,  indicative  of 
tough,  strong  material,  is  crystalline,  and  the  fracture  shows 
a  decided  brittleness. 

According  to  Prof.  J.  B.  Johnson,  there  are  three  well- 
recognized  causes  of  this  crystalline  structure,  indicative  of 
inferior  material. 

"  First,  the  so-called  wrought  iron  may  have  been  rolled 
from  fagotted  scrap,  some  of  which  was  probably  high-carbon 
steel,  and  this  portion  would  show  a  crystalline  fracture. 

"  Second,  the  puddle-ball  may  have  been  formed  under  too 
great  a  heat  (a  common  fault),  so  that  a  portion  of  it  had 
been  actually  melted,  thus  forming  of  this  portion  ingot  metal 
or  steel,  which  part  would,  when  cold,  be  wholly  crystal- 
line. 

"Third,  the  puddling  process  may  have  been  incomplete, 
when,  with  a  low  fire,  some  of  the  unreduced  pig  iron  would 
be  removed  from  the  ball,  and  this  would  form  a  coarsely 
crystalline  portion  of  the  final  rolled  bar." 

Steel  manufactured  for  constructive  purposes  is  at  present 
produced  by  one  of  two  processes:  either  the  ''Bessemer" 
or  converter,  or  by  the  "open-hearth"  or  furnace  method. 
From  the  character  of  the  lining  of  the  converter  or  furnace 
being  either  acid  or  basic,  a  further  distinctive  technical  term 
of  "  acid"  or  "basic  Bessemer,"  or  "  acid  "  or  "  basic  open- 
hearth  steel"  is  commercially  used. 


36  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

Physical    Differences    between    Iron    and    Steel. — The 

metamorphose  of  cast  iron  into  steel  is  produced,  as  is  the  case 
with  the  refinement  of  iron,  by  oxidation  as  the  principal  fac- 
tor. Made  from  the  same  material,  and  transformed  by  sim- 
ilar chemical  agencies,  it  is  not  surprising  that  there  is  a  great 
similarity  of  the  two  finished  products,  one  termed  wrought 
iron  and  the  other  structural  steel.  The  difficulty  of  defining 
steel  and  the  narrow  line  separating  it  from  iron  is  clearly  put 
in  the  "Manufacture  and  Properties  of  Structural  Steel"  as 
follows : 

' '  Prior  to  the  development  of  the  Bessemer  and  open-hearth 
processes  there  was  little  room  for  disagreement  as  to  the  di- 
viding line  between  iron  and  steel.  If  it  would  harden  in 
water  it  was  steel ;  if  not,  it  was  wrought  iron.  When  the 
modern  methods  were  introduced,  a  new  metal  came  into  the 
world.  In  its  composition  and  in  its  physical  qualities  it  was 
exactly  like  many  steels  of  commerce,  and  naturally  and  right- 
ly it  was  called  steel.  By  degrees  these  processes  widened 
their  field,  and  began  to  make  a  soft  metal  which  possessed 
many  of  the  characteristics  of  ordinary  wrought  iron,  and 
which  was  not  made  by  any  radical  changes  in  methods,  but 
simply  by  the  use  of  a  rich  ferro-manganese.  Notwithstanding 
this  fact,  some  engineers  claimed  that  the  new  metal  was  not 
steel,  but  iron.  The  makers  replied  that  it  was  made  by  the 
same  process  as  hard  steel,  and  that  it  was  impossible  to  draw  a 
line  in  the  series  of  possible  and  actual  grades  of  product  which 
they  made."  Mr.  Howe,  in  his  *'  Metallurgy  of  Steel , "  says, 
"  The  terms  Iron  and  Steel  are  employed  so  ambiguously  and 
inconsistently  that  it  is  to-day  impossible  to  arrange  all  varie- 
ties under  a  simple  and  consistent  classification."  Continuing 
to  quote  from  the  "  Manufacture  and  Properties  of  Structural 
Steel,"  "It  is  true,  as  argued  by  Mr.  Howe,  that  many  of 
the  common  products  of  metallurgy  and  art  shade  impercept- 
ibly into  one  another ;  but  it  is  surely  extraordinary  when  the 


. 
PROPERTIES   OF  STRUCTURAL   METALS. 


37 


dividing  line  can  not  be  drawn  even  in  theory,  much  less  in 
practice;  when,  wherever  it  falls,  it  must  divide,  not  inter- 
mediate, but  finished  products,  used  in  enormous  quantities, 
and  blending  into  one  another  by  insensible  gradations,  and 
when  every  shade  of  these  variations  is  the  subject  of  rigorous 
engineering  specifications." 

It  is  customary  and  necessary,  in  ordering  steel,  to  give  a 
certain  margin  in  filling  specifications,  and  it  will  be  evident, 
no  matter  how  close  this  margin  is,  that  if  a  line  could  be  drawn, 
it  would  not  infrequently  happen  that  he  who  ordered  ingot 
iron  would  receive  steel,  and  he  who  ordered  steel  would  re- 
ceive ingot  iron. 

Many  different  tests  have  been  proposed  at  various  times 
for  determining  the  mechanical  properties  of  steels,  but  al- 
though some  of  them  are  of  value  in  special  cases,  the  one 
method  of  investigation  which  has  become  well  nigh  universal 
is  to  break  by  a  tensile  stress  and  measure  the  ultimate 
strength,  the  elastic  limit,  the  elongation,  and  the  reduction  of 
area.  Strictly  speaking,  none  of  these  properties  has  any  direct 
connection  with  hardness,  and  it  is  also  true  that  in  special  in- 
stances, as  with  very  high  carbons,  hardening  may  reduce  the 
tensile  strength  by  the  creation  of  abnormal  internal  strains; 
but  in  all  ordinary  steels  it  is  certain  that  hardening  is  accom- 
panied by  an  increase  of  strength,  by  an  exaltation  of  the  elas- 
tic limit,  and  a  degree  in  ductility. 

"  The  fact  that  common  soft  steel  is  materially  strengthened 
by  chilling  has  been  widely  recognized  for  many  years,  but  the 
extent  of  the  alteration  in  physical  properties  in  the  softest 
and  purest  metals  is  not  generally  understood." 

The  table  on  page  17  shows  the  results  of  a  series  of  tests 
made  by  Mr.  H.  H.  Campbell. 

Again  from  "  Manufacture  and  Properties  of  Structural 
Steel  "  : 

tl  The  classification   by  hardening  is  a  dead   issue  in  our 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 


country.  It  had  quietly  passed  away  unnoticed  and  un- 
known before  the  committee  of  the  Mining  Engineers  had 
met,  and  the  best  efforts  of  that  brilliant  galaxy  of  talent  could 
only  produce  a  kindly  eulogy." 

EFFECT   OF   QUENCHING    ON    THE    PHYSICAL    PROPERTIES 
OF    DIFFERENT    SOFT    STEELS.. 

NOTE.— Bars  were  2  in.  X  I  in.  flats,  rolled  from  6  in.  X  6  in.  ingot,  and  were  chilled  at  a 
dull  yellow  heat. 


Number  of  Test-bar 

1 

2 

8 

4 

5 

6 

Composition,  per  cent. 

Carbon. 
Manganese. 
Phosphorus. 
Sulphur. 

.09 
•44 
.on 
•033 

49390 
66080 

.12 
•32 
.004 
.027 

.11 
•43 

.010 

.010 

.12 

»-32 

.004 
.027 

.eg 

•39 
.017 
.031 

.10 

.16 

.010 

.019 

Ultimate  strength, 
pounds  per  square  inch  f 

Natural. 
Quenched. 

48960 
65670 

48960 
66300 

48260 
63640 

32340 
50170 

497^0 
62280 

46250 
58380 

29830 
40500 

64.50 
69-38 

Elastic  limit,  pounds  per  1 
square  inch.                       f 

Natural. 
Quenched. 

Natural. 
Quenched. 

33220 
47310 

67.26 
71.60 

33390 

33010 

31040 
46580 

Elastic  ratio,  per  cent. 

68.20 

67.42 

67.01 
78-83 

62.38 
74-79 

Elongation  in  8  in.,  in  per  | 
cent.                                   | 

Natural. 
Quenched. 

29-75 
18.75 

31.00 
16.25 

32-50 
15.00 

32.50 

17-75 

55-75 
64.47 

31-25 
23-75 

37-75 
27.50 

68.38 
68.97 

Reduction    of    area,    per  I 
cent.                                   ) 

Natural. 
Quenched. 

50.80 
56.50 

52-5° 
63.27 

54.10 
63-47 

49.00 
65  '!5 

"  Strictly  speaking,  some  mention  must  be  made  of  hard- 
ening in  a  complete  and  perfect  definition,  for  it  is  possible  to 
make  steel  in  a  puddling-furnace  by  taking  out  the  viscous 
mass  before  it  has  been  completely  decarburized ;  but  this 
crude  and  unusual  method  is  now  a  relic  of  the  past,  and  may 
be  entirely  neglected  in  practical  discussion. 

"  No  attempt  will  be  made  here  to  give  any  iron-clad  for- 
mula, but  the  following  statements  portray  the  current  usage  in 
our  country : 

"  (i)  By  the  term  '  wrought  iron  '  is  meant  the  product  of 
the  puddling-furnace  or  the  sinking-fire. 

"  (2)  By  the  term  'steel'  is  meant  the  product  of  the  cemen- 
tation process,  or  the  malleable  compounds  of  iron  made  in 
the  crucible,  the  converter,  or  the  open-hearth  furnace." 


PROPERTIES   OF  STRUCTURAL   METALS.  39 

Effect  of  Heating. — The  changes  produced  in  the  physical 
properties  of  steel  through  reheating  and  chilling  by  quench- 
ing are  radical ;  little  less  so  is  the  effect  produced  by  anneal- 
ing, or  the  tempering  of  steel  by  reheating  as  in  shop-work, 
where  the  metal,  after  being  heated  for  rolling  or  bending,  is 
allowed  to  cool  gradually. 

The  average  extent  of  the  changes  thus  produced  is  shown 
from  the  tests  made  by  Mr.  H.  H.  Campbell  upon  specimens 
both  of  Bessemer  and  open-hearth  steels,  and  recorded  as 
follows : 

"  The  decrease  in  ultimate  strength  by  annealing  the  Bes- 
semer bars  averaged  4175  pounds  per  square  inch  in  the 
rounds  and  5683  pounds  in  the  flats,  while  the  open-hearth 
was  lowered  5134  pounds  in  the  rounds  and  7649  in  the  flats. 

"  In  this  important  and  fundamental  quality  the  two  kinds 
of  steel  are  very  similarly  affected,  but  in  other  particulars 
there  seems  to  be  a  radical,  difference  which  is  difficult  to  ex- 
plain. The  elongation  of  the  Bessemer  steel  is  increased  by 
annealing  in  every  case  except  two,  the  average  being  1.33 
per  cent.,  while  the  open-hearth  metal  shows  a  loss  in  three 
cases,  with  an  average  loss  for  all  cases  of  o.2i'per  cent.  This 
is  not  very  conclusive,  but  there  is  a  more  marked  difference 
in  the  reduction  of  area,  for  in  the  Bessemer  steel  there  is  an 
increase  in  the  annealed  bar  in  every  case  varying  from  7  to 
15.18  per  cent.,  while  the  open-hearth  showed  an  increase  in 
only  three  cases,  the  maximum  being  2.81  per  cent.,  and  a 
•decrease  in  five  cases,  the  greatest  loss  being  7«2O  per  cent." 

The  results  arrived  at  by  Mr.  Campbell  after  exhaustive 
tests,  comparing  the  effect  upon  both  Bessemer  and  open- 
hearth  steels,  are  as  follows :  ' '  Annealing  is  useful  in  removing 
the  strains  caused  by  distortion,  for  in  such  cases  the  gain  in 
safety  more  than  counterbalances  the  loss  of  strength,  but  it  f 
may  be  accepted  as  a  general  rule  that  steel  is  in  its  best  con- 
dition when  it  leaves  the  rolling-mill;  that  the  shop  treatment 


40  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

should  retain,  as  far  as  possible,  the  natural  qualities  of  the 
metal;  and  that  the  bar  should  be  heated  only  when  it  is 
necessary  to  make  a  permanent  bend." 

Constructive  or  soft  steel  is  produced,  as  has  been  stated, 
by  one  of  two  processes,  the  Bessemer  and  the  open-hearth, 
and  a  technical  classification  of  the  product  is  determined  by 
the  character  of  the  lining  employed  in  the  furnace,  whether 
acid  or  basic.  An  authentic,  brief,  and  comprehensive  state- 
ment descriptive  of  the  two  general  methods  of  manufacturing 
structural  steels  is  copied  in  full  from  the  work  so  frequently 
herein  quoted,  and  is  as  follows : 

Bessemer  Steel. — "  The  acid-Bessemer  process  consists  in 
blowing  air  into  liquid  pig  iron  for  the  purpose  of  burning  most 
of  the  silicon,  manganese,  and  carbon  of  the  metal,  the  opera- 
tion being  conducted  in  an  acid-lined  vessel,  and  in  such  a  man- 
ner that  the  product  is  entirely  fluid.  The  way  in  which  the 
air  is  introduced  is  a  matter  of  little  importance  as  far  as  the 
character  of  the  product  is  concerned.  .  .  .  The  lining  is  made 
of  either  stone  or  brick,  or  other  refractory  material,  and  is 
about  one  foot  thick.  .  .  .  The  blast  is  kept  at  a  pressure  of 
from  25  to  30  pounds  per  square  inch  during  the  first  part  of 
the  blow,  but,  in  the  case  of  a  very  hot  charge,  or  if  the  slag  is 
sloppy,  the  pressure  must  sometimes  be  reduced  to  10  pounds 
after  the  flame  '  breaks  through  '  (i.e.,  after  the  carbon  begins 
to  burn),  '  to  prevent  the  expulsion  of  the  metal  from  the 
nose  .  .  .  the  heats,  whether  light  or  heavy,  are  usually  blown 
in  from  7  to  12  minutes.' ' 

After  the  chemical  change  has  taken  place  whereby  the 
cast  iron  has  become  molten  steel,  the  fluid  metal  is  tapped  or 
drawn  off  into  cast-iron  moulds,  where  the  metal  solidifies  so 
that  it  may  be  handled,  when  it  is  then  called  an  ingot,  and, 
as  such,  reheated  in  a  furnace,  passed  through  trains  of  rolls, 
as  is  the  case  with  wrought  iron,  and  rolled  into  the  desired 
shape. 


PROPERTIES   OF  STRUCTURAL   METALS.  41 

The  basic  Bessemer  process  is  identical  with  that  just 
described,  except  the  converter  or  furnace  is  lined  with  a  ma- 
terial that  resists  the  action  of  the  basic  slags.  Again  quoting 
from  the  4<  Manufacture  and  Properties  of  Structural  Steel  "  : 
"This  lining  is  usually  made  of  dolomite,  but  sometimes  a 
limestone  is  used  containing  a  very  small  proportion  of  magne- 
sia. The  stone  must  be  burned  thoroughly  to  expel  the  last 
trace  of  volatile  matter,  and  then  ground  and  mixed  with  an- 
hydrous tar.  The  highest  function  of  the  lining  is  to  remain 
unaffected,  and  allow  the  basic  additions  to  do  their  work 
alone,  so  that  the  rapid  destruction  of  a  basic,  as  compared 
with  an  acid  lining,  is  not  due  to  any  necessary  part  it  plays 
in  the  operation,  but  to  the  fact  that  there  is  no  basic  material 
in  nature  which  is  plastic,  and  which  by  moderate  heating  will 
give  the  firm  bond  that  makes  clay  so  valuable  in  acid  practice.'' 

Acid  and  basic  Bessemer  steel  is  sometimes  known  as  con- 
verter steel,  and  depending  largely  upon  the  product  of  the 
blast-furnace,  as  well  as  the  possibility  of  large  output,  the  cost 
of  production  of  Bessemer  steels  is  considerably  less  than  the 
product  of  the  open-hearth  process,  which  finds  it  advantageous 
to  use  a  considerable  proportion  of  scrap  steel,  and  is  more 
limited  in  the  matter  of  its  output.  It  is  claimed  by  many 
authorities  that  the  metallurgical  conditions  are  such  that  a 
greater  degree  of  certainty  in  the  production  of  open-hearth  is 
possible,  and,  whether  this  be  true  or  not,  the  fact  remains 
that  the  general  tendency  among  engineers  and  as  evidenced 
by  numerous  recent  specifications,  is  to  give  a  preference  to 
the  open-hearth  product  over  Bessemer  steels. 

A  description  of  the  process  of  manufacture  of  the  open- 
hearth  product  is  as  follows,  and  is  also  from  Mr.  Campbell's 
admirable  work: 

Open- hearth  Steel. — "  The  open-hearth  process  consists  of 
melting  pig  iron,  mixed  with  more  or  less  wrought  iron,  steel, 
or  similar  iron  products,  by  exposure  to  the  direct  action  of 


42  TOWERS  AND    TANKS  fOR    WATER-WORKS. 

the  flame  in  a  regenerative  furnace,  and  converting  the  result- 
ant bath  into  steel,  the  operation  being  so  conducted  that  the 
final  product  is  entirely  fluid." 

As  stated,  this  regenerative  furnace  steel  is  classified  as 
acid  or  basic,  depending  upon  the  formation  or  texture  of  the 
lining. 

"  In  one  the  hearth  is  lined  with  sand,  and  the  slag  is  sili- 
cious;  in  the  other  the  hearth  is  made  of  such  material  that  a 
basic  slag  can  be  carried  during  the  operation." 

As  is  the  case  with  wrought  iron,  the  metalloids  as  carbon, 
silicon,  sulphur,  manganese  and  phosporus  affect  the  finished 
product,  carbon  being  the  least  uncertain  and  detrimental  of 
the  alloys,  for  structural  steel  being  a  carbon  steel,  its  presence 
should  possibly  not  be  limited.  Also  as  with  iron,  the  most 
important  of  the  metalloids  are  sulphur  and  phosphorus,  the  last 
being  the  most  to  be  feared.  Regarding  the  effect  of  sulphur 
on  steel  products,  Mr.  Campbell  says:  "Nothing  is  better 
established  than  the  fact  that  sulphur  injures  the  rolling  quali- 
ties of  steel,  causing  it  to  crack  and  tear,  and  lessening  its 
capacity  to  weld.  ...  In  the  making  of  common  steel  for 
simple  shapes,  a  content  of  .10  per  cent,  is  possible,  and  may 
even  be  exceeded  if  great  care  be  taken  in  the  heating,  but  for 
rails  and  other  shapes  having  thin  flanges  it  is  advantageous  to 
have  less  than  .08  per  cent.,  while  every  decrease  below  this 
point  is  seen  in  a  reduced  number  of  defective  bars." 

Effects  of  Phosphorus. — The  effects  of  phosphorus,  the 
most  potent  of  all  the  metalloids  for  evil,  is  thus  given  by  Mr. 
Campbell:  "Of  all  the  elements  commonly  found  in  steel, 
phosphorus  stands  pre-eminent  as  the  most  undesirable. 
It  is  objectionable  in  the  rolling-mill,  for  it  tends  to  produce 
coarse  crystallization,  and  hence  lowers  the  temperature  to 
which  it  is  safe  to  heat  the  steel,  and,  for  this  reason,  phos- 
phoritic  metal  should  be  finished  at  a  lower  temperature  than 
pure  steel  in  order  to  prevent  the  formation  of  a  crystalline 


. 


PROPERTIES   OF  STRUCTURAL   METALS.  43 

structure  during  cooling.  Aside  from  these  considerations  its 
influence  is  not  felt  in  a  marked  degree  in  the  rolling-mill,  for 
it  has  no  disastrous  effect  upon  the  toughness  of  red-hot 
metal  when  the  content  does  not  exceed  .  15  per  cent." 

A  discussion  of  the  effects  of  phosphorus  in  steel  by 
Howe's  "  Metallurgy  of  Steel,"  and  summarized  by  Mr. 
Campbell,  is  as  follows: 

"(i)  The  effect  of  phosphorus  on  the  elastic  ratio,  as  on 
elongation  and  contraction,  is  very  capricious. 

"(2)  Phosphoric  steels  are  liable  to  break  under  very 
slight  tensile  stress  if  suddenly  or  vibratorily  applied. 

"  (3)  Phosphorus  diminishes  the  ductility  of  steel  under  a 
gradually  applied  load  as  measured  by  its  elongation,  contrac- 
tion, and  elastic  ratio  when  ruptured  in  an  ordinary  testing- 
machine,  but  it  diminishes  its  toughness  under  shock  to  a  still 
greater  degree,  and  this  it  is  that  unfits  phosphoric  steels  for 
most  purposes. 

"(4)  The  effect  of  phosphorus  on  static  ductility  appears 
to  be  very  capricious,  for  we  find  many  cases  of  highly  phos- 
phoric steel  which  show  excellent  elongation,  contraction,  and 
even  fair  elastic  ratio,  while  side  by  side  with  them  are  others 
produced  under  apparently  identical  conditions  but  statically 
brittle. 

"(5)  If  any  relation  between  composition  and  physical 
properties  is  established  by  experience,  it  is  that  of  phosphorus 
in  making  steel  brittle  under  shock;  and  it  appears  reason- 
ably certain,  though  exact  data  sufficing  to  demonstrate  it  are 
not  at  hand,  that  phosphoric  steels  are  liable  to  be  very  brittle 
under  shock,  even  though  they  maybe  tolerably  ductile  static- 
ally. The  effects  of  phosphorus  on  shock-resisting  power, 
though  probably  more  constant  than  its  effects  on  static  duc- 
tility, are  still  decidedly  capricious.  .  .  ." 

Mr.  Campbell's  conclusion  in  regard  to  the  effects  of 
phosphorus  in  the  composition  of  steel,  and  the  limit  to  be 


44  TOWERS  AND    TANKS   FOR    WATER-WORKS. 

placed  upon  its  presence,  is  as  follows:  "No  line  can  be 
drawn  that  shall  be  called  the  limit  of  safety,  since  no  practi- 
cal test  has  ever  been  devised  which  completely  represents  the 
effect  of  incessant  tremor.  For  common  structural  materials 
the  critical  content  has  been  placed  at  .10  per  cent,  by  general 
consent,  but  this  is  altogether  too  high  for  railroad-bridge 
work.  All  that  can  be  said  is  that  safety  increases  as 
phosphorus  decreases,  and  the  engineer  may  calculate  just 
how  much  he  is  willing  to  pay  for  greater  protection  from 
accident." 

To  what  extent  specifications  calling  for  reduction  of  this 
element  affect  the  market  price  of  materials  is  shown  from 
the  following,  taken  from  Prof.  Pence's  "  Stand-pipe  Acci- 
dents and  Failures  " : 

"  A  recent  proposal  for  the  construction  of  an  important 
stand-pipe  in  a  Western  city  included  bids  according  to  five 
limitations  for  phosphorus,  running  from  0.08  to  0.04  per 
cent,  inclusive.  The  relative  bids  on  the  superstructure  for 
the  several  grades  of  steel,  taking  that  for  the  highest  phos- 
phorus limit  as  unity,  were  as  follows: 

Phosphorus  Limit.  Relative  Bid. 

0.08 1. 00 

O.O/ 1 .03 

O.O6 I. O8 

0.05 I.I/ 

0.04 1.23 

"  The  plates  were  to  be  '  soft,  acid,  open-hearth  steel,'  of 
54,000  to  62,000  Ibs.  per  sq.  in.  in  tensile  strength;  elastic 
limit,  31,000  Ibs.  persq.  in.  ;  minimum  elongation  in  8  inches, 
26$;  minimum  reduction  of  area,  50$;  cold  bent  flat;  and 
not  more  than  0.08$  phosphorus,  and  less  per  cent,  as  per 
detailed  bid." 

Standard  specifications  for  structural  steel  have  been 
adopted  in  the  United  States  as  follows: 


PROPERTIES   OF  STRUCTURAL   METALS.  45 

MANUFACTURERS'   STANDARD   SPECIFICATIONS. 

STRUCTURAL   STEEL. 

1.  Process  of  Manufacture. — Steel  may  be  made  by  either  the  open- 
hearth  or  Bessemer  process. 

2.  Testing. — All  tests  and  inspections  shall  be  made  at   place   of 
manufacture  prior  to  shipments. 

3.  Test-pieces. — The  tensile  strength,  limit  of  elasticity,  and  ductility, 
shall  be  determined  from  a  standard  test-piece  cut  from  the  finished  ma- 
terial.    The  standard  shape  of  the  test-piece  for  sheared  plates  shall  be 
as  shown  by  the  following  sketch  : 


U- -ParaHel-8ecHon-nofr4e8Mhaiir9- 


*j 


<&*-- l-"-4--l"-4--l"-i^..._            ^    Piece  to  be  of  same  thickness  as  Plate 
I*"""  aboutHL'8 — — -— -W 

On  tests  cut  from  other  .material  the  test-piece  may  be  either  the  same 
as  for  plates,  or  it  may  be  planed  or  turned  parallel  throughout  its  entire 
length. 

The  elongation  shall  be  measured  on  an  original  length  of  8  ins., 
except  when  the  thickness  of  the  finished  material  is  T5^  in.  or  less,  in 
which  case  the  elongation  shall  be  measured  in  a  length  equal  to 
sixteen  times  the  thickness;  and,  except  in  rounds  of  f  in.  or  less  in 
diameter,  in  which  case  the  elongation  shall  be  measured  in  a  length 
equal  to  eight  times  the  diameter  of  section  tested.  Two  test-piece 
shall  be  taken  from  each  melt  or  blow  of  finished  material,  one  for  ten- 
sion and  one  for  bending. 

4.  Annealed  Test-pieces. — Material  which  is  to  be  used  without  anneal- 
ing or  further  treatment  is  to  be  tested  in  the  condition  in  which  it 
comes  from  the  rolls.     When  material  is  to  be  annealed  or  otherwise 
treated  before  use,  the  specimen  representing  such   material  is  to  be 
similarly  treated  before  testing. 

5.  Marking. — Every  finished  piece  of  steel  shall  be  stamped  with  the 
blow-  or  melt-number,  and  steel  for  pins  shall  have  the  blow-  or  melt- 
number  stamped  upon  the  ends.      Rivet   and    lacing  steel,  and    small 
pieces  for  pin-plates  and  stiffeners,  may  be  shipped  in  bundles  securely 
wired  together,  with  the  blow-  or  melt-number  on  a  metal  tag  attached. 

6.  Finish. — Finished  bars  must  be  free  from  injurious  seams,  flaws, 
or  cracks,  and  have  a  workmanlike  finish. 


46  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

7.  Chemical  Properties. — Steel  for  railway  bridges  :  Maximum  phos- 
phorus, .08  per  cent.     Steel  for  buildings,  train-sheds,  highway  bridges, 
and  similar  structures  :  Maximum  phosphorus,  .10  per  cent. 

8.  Physical  Properties. — Steel  shall  be  of  three  grades,  rivet,  soft,  and 
medium. 

9.  Rivet  Steel. — Ultimate    strength,  48,000    to    58,000    pounds  per 
square  inch. 

Elastic  limit,  not  less  than  one-half  the  ultimate  strength. 
Elongation,  26  per  cent. 

Bending  test,  180  degrees  flat  on  itself,  without  fracture  on  outside  of 
bent  portion. 

10.  Soft    Steel. — Ultimate    strength,    52,000    to    62,000   pounds   per 
square  inch. 

Elastic  limit,  not  less  than  one-half  the  ultimate  strength. 
Elongation,  25  per  cent. 

Bending  test,  1 80  degrees  flat  on  itself,  without  fracture  on  outside 
of  bent  portion. 

11.  Medium  Steel. — Ultimate  strength,  60,000  to  70,000  pounds  per 
square  inch. 

Elastic  limit,  not  less  than  one-half  the  ultimate  strength. 
Elongation,  22  per  cent. 

Bending  test,  180  degrees  to  a  diameter  equal  to  thickness  of  piece 
tested,  without  fracture  on  outside  of  bent  portion. 

12.  Pin  Steel. — Pins  made  from  either  of  the  above-mentioned  grades 
of  steel  shall,  on  specimen  test-pieces  cut  at  a  depth  of  one  inch  from 
surface  of  finished  material,  fill  the  physical  requirements  of  the  grade 
of  steel  from  which  they  are  rolled,  for  ultimate  strength,  elastic  limit, 
and  bending,  but  the  required  elongation  shall  be  decreased  5  per  cent. 

13.  Eye-bar  Steel. —  Eye-bar  material,  \\  inches  and  less  in  thickness, 
made  of  either  of  the  above-mentioned  grades  of  steel,  shall,  on  test- 
pieces  cut  from  finished  material,  fill  the  requirements  of  the  grades  of 
steel  from  which  it  is  rolled.     For  thickness  greater  than    \\  inches, 
there  will  be  allowed  a  reduction  in  the  percentage  of  elongation  of  i  per 
cent,  for  each  \  of  an  inch  increase  of  thickness,  to  a  minimum  of  20  per 
cent,  for  medium  steel  and  22  per  cent,  for  soft  steel. 

14.  Full-size  Test  of  Steel  Eye-bars. — Full-size  test  of  steel  eye-bars 
shall  be  required  to  show  not  less  than   10  per  cent,  elongation  in  the 
body  of  the  bar,  and  tensile  strength  not  more  than  5000  pounds  below 
the  minimum  tensile  strength  required  in  specimen  tests  of  the  grade  of 
steel  from  which  they  are  rolled.     The  bars  will  be  required  to  break  in 
the  body,  but  should  a  bar  break  in  the  head,  but  develop  10  per  cent 
elongation  and  the  ultimate  strength  specified,  it  shall  not  be  cause  for 


PROPERTIES   OF  STRUCTURAL   METALS. 


47 


rejection,  provided  not  more  than  one-third  of  the  total  number  of  bars 
tested  break  in  the  head  ;  otherwise  the  entire  lot  will  be  rejected. 

15.  Variation  in  Weight, — The  variation  in  cross-section  or  weight 
of  more  than  2\  per  cent,  from  that  specified  will  be  sufficient  cause  for 
rejection,  except  in  the  case  of  sheared  plates,  which  will  be  covered  by 
the  following  permissible  variations  : 

(a)  Plates  12^  pounds  or  heavier,  when  ordered  to  weight,  shall  not 
average  more  variation  than   2^  per  cent,  either  above  or  below  the 
theoretical  weight. 

(b)  Plates  from  10  to  12^  pounds,  when  ordered  to  weight,  shall  not 
average  a  greater  variation  than  the  following: 

Up  to  75  inches  wide,  i\  per  cent.,  either  above  or  below  the  theoret- 
ical weight. 

Seventy-five  inches  and  over,  5  per  cent.,  either  above  or  below  the 
theoretical  weight. 

(c)  For  all  plates  ordered  to  gauge  there  will  be  permitted  an  average 
excess  of  weight  over  than  corresponding  to  the  dimensions  in  the  order 
equal  in  amount  to  that  specified  in  the  following  table.    . 

TABLE  OF  ALLOWANCES  FOR  OVERWEIGHT  FOR  RECTANGULAR  PLATES 
WHEN  ORDERED  TO  GAUGE. 


Thickness 
of 
Plate. 

Width  of  Plate. 

Thickness 
of 
Plate. 

Width  of  Plate. 

Up  to 
75  in- 

75  in.  to 
100  in. 

Over 

100  in. 

Up  to 
50  in. 

50  in. 
and  above. 

15  per  cent- 

»i  ;; 

IO 

1/4  inch. 

5/'6 
3/8 
7/16 

1/2 

9/16 

10  per  cent. 

I      » 
J»      ;: 

14  per  ce 

12 
IO 

8 
7 
6* 

nt. 

18  p 
16 
13 

IO 

9 

I* 

:r  ce 

it. 

1/8  up  to  5/32 
5/32  "   ;'  3/16 
3/'6"    "   1/4 

10  per  cent. 

8J  " 

7     " 

Over  5/8      " 

3*  "        " 

5     " 

6*  " 

Work  of  International  Association. — An  effort  is  being 
made  at  this  time  by  the  International  Association  for  Test- 
ing Materials,  to  establish  international  standard  specifica- 
tions for  the  inspection  of  iron  and  steel.  Each  national 
branch  will  contribute  to  the  grand  council  a  committee 
report,  dealing  in  part  with  "Determination  of  Methods  of 
Testing  the  Homogeneity  of  Iron  and  Steel,  looking  to  their 
Eventual  Use  for  Inspection,"  and  from  these  reports  a  new 


48  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

set  of  standard  specifications  may  be  evolved,  but  whether  in 
general  practice  they  are  to  supersede  those  employed  at  this 
time  is,  of  course,  entirely  conjectural. 

Some  little  time  since  the  American  Division  of  the 
International  Committee  submitted  a  tentative  report,  sub- 
ject to  further  consideration  and  discussion  before  final 
action  is  taken  at  a  meeting  called  for  October.  So 
universally  has  this  report  been  endorsed  and  so  favorably 
received,  that  the  possibility  seems  that  it  will  not  be  mater- 
ially modified,  and  that  it  will  receive  the  approval  of  the  In- 
ternational Committee  and  spring  into  general  use  throughout 
the  civilized  world.  It  is  interesting  to  note  that,  in  treating 
of  structural  material,  its  introductory,  defining  the  process  of 
manufacture,  advocates  a  radical  departure  from  the  "  Manu- 
facturers' Standard  Specifications  "  in  that  it  eliminates  the 
Bessemer  process  of  manufacture,  requiring  that  "Steel  shall 
be  made  by  the  open-hearth  process."  This  is  not  such  a 
radical  departure  as  it  would  seem  upon  the  surface,  as  prior 
to  this  report,  the  tendency  toward  a  preference  for  this 
product  was  everywhere  in  evidence,  and  had  become  a  com- 
mercial possibility  through  the  erection  of  numerous  open- 
hearth  plants  of  large  capacities,  an  immense  impetus  having 
been  given  this  method  of  production  by  the  successful  com- 
mercial development  of  the  open-hearth  continuous  process, 
permitting  the  use  of  fluid  metal  from  blast-furnaces,  mixers, 
and  cupolas.  Altogether,  the  "signs  of  the  times"  dis- 
tinctly point  to  the  increased  production  of  open-hearth  steel 
for  structural  materials,  possibly  to  the  complete  elimination 
of  the  Bessemer  method  of  manufacture. 

For  some  time  past  efforts  have  been  made  by  various  tech- 
nical associations  to  bring  about  a  harmonious  agreement  looking 
toward  the  formulation  and  adoption  of  standard  specifications 
for  iron  and  steel,  and  although  a  general  acceptance  and  agree- 
ment has  not  yet  been  concluded,  along  with  the  present  tendency 


PROPERTIES   OF  STRUCTURAL   METALS.  49 

toward  standardization,  tentative  acceptance  of  some  important 
changes  in  the  present  Manufacturers'  Standard  has  been  pre- 
sented and  is  meeting  with  favor  from  those  interested. 

The  most  important  of  the  changes  made  relates  to  the  adop- 
tion of  a  single  standard  grade  of  structural  steel  for  all  purposes 
of  60,000  Ibs.  tensile  strength,  with  an  allowable  variation  of 
5000  Ibs.  either  way,  and  the  omission  of  any  requirement  as 
to  reduction  of  area  and  elastic  limit.  It  is  also  strongly  urged 
that  more  importance  should  be  given  to  cold-bend  test,  either 
plain  or  nickelled,  of  full-sized  sections.  The  outcome  of  this 
movement  will  be  watched  with  interest. 


CHAPTER  III. 
THE  USE  OF  IRON. 

NOTWITHSTANDING  the  inability  of  metallurgists  to  de- 
termine with  certainty  the  precise  point  in  its  evolution  when 
iron  is  converted  into  steel,  and  conceding  scientific  uncer- 
tainty as  to  technical  definition,  the  well-known  character- 
istics of  iron  and  steel  exhibit  radical  differences,  and  prac- 
tical metal-workers  seldom  err  in  determining  each  with  cer- 
tainty ;  therefore  comparison  is  entirely  pertinent  in  consider- 
ing both  metals  as  materials  for  stand-pipe  construction,  and 
the  individual  merits  of  each,  referring  to  general  utility,  fit- 
ness, and  comparative  cost,  should  receive  consideration. 

Until  1880  iron  plate  was  used  almost  exclusively  in  the 
construction  of  metallic  reservoirs,  although  a  steel  pipe  is 
recorded  as  having  been  erected  as  early  as  1876,  about  which 
time  the  commencement  of  the  steel  industry  in  the  United 
States  may  be  said  to  have  dated.  From  that  time  the  in- 
troduction of  metallic  members  in  structures  slowly  and  tim- 
idly advanced,  criticised  at  each  step ;  but,  profiting  by  each 
failure,  overcame  the  difficulty  until  at  the  present  time  few 
mills  continue  the  practice  of  rolling  iron  shapes  and  plates  for 
structural  work,  and  specifications  calling  for  ferric  members 
are  now  practically  obsolete. 

The  United  States  Statistical  Bureau  of  the  Treasury  De- 
partment, for  the  year  1899,  places  the  United  States  at  the 
head  of  the  steel  and  iron  producing  countries  of  the  world, 
with  a  record  of  13,620,703  tons  .of  pig  iron  produced,  of 
which  78.1  per  cent.,  or  10,639,857  tons,  was  converted  into 
steel. 

50 


THE    USE    OF  IRON.  51 

The  Change  to  Steel. — The  underlying  cause  for  a 
change  so  radical  as  to  amount  to  an  industrial  revolution,  is 
the  appreciation  and  realization  of  the  commercial  and  con- 
structive value  of  steel,  leading  to  scientific  advance  constant- 
ly improving  the  physical  and  chemical  properties,  whilst  the 
increased  demand  introduced  new  facilities  for  reducing  the 
price  of  the  product  below  that  of  commercial  wrought  iron. 
As  has  been  stated,  at  this  time,  of  the  992  metallic  reservoirs 
in  the  United  States,  220  are  of  iron  and  292  of  steel, 
leaving  480  undefined.  Whilst  these  records  give  only  a 
small  excess  of  steel  as  compared  with  iron  structures,  the 
increased  use  of  steel  is  more  apparent  when  it  is  considered 
that  only  within  the  past  few  years  has  steel  been  recognized 
as  a  suitable  metal  for  such  work. 

Classification  of  Failures. — From  the  best  procurable 
records  amongst  the  entire  number  of  metallic  reservoirs  of 
water-supply  plants  in  this  country,  there  are  recorded  54  partial 
and  complete  failures  and  collapses,  17  of  which  are  credited 
to  steel  structures,  whilst  only  7  known  to  have  been  built  of 
iron  plates  have  failed.  From  this  it  would  seem  that  steel 
tanks  are  more  liable  to  collapse  than  iron  ones,  but  this  fact 
should  only  be  admitted  conditionally  and  after  consideration 
of  the  causes  inducing  the  failures. 

Of  the  17  complete  and  partial  failures  attributed  to  the 
list  of  steel  tanks,  the  date  of  erection  and  failure  shows  the 
majority  of  them  to  have  been  constructed  during  what  might 
be  termed  the  experimental  stage  of  steel-production,  as,  for 
instance,  chemical  analysis  of  the  steel  used  in  four  of  these 
tanks  shows  a  large  proportion  of  phosphorus — in  one  case  as 
high  as  0.162$,  which  would  certainly  have  caused  the  plate 
to  be  rejected  at  this  time,  unless  its  use  were  dictated  by  dis- 
tinctly dishonest  conditions. 

Again,  a  consideration  of  the  circumstances  and  a  study  of 
the  prevailing  conditions  and  designs,  show  three  of  the  re- 


52  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

ported  pipes  to  have  been  of  most  unusual  and  eccentric  de- 
sign, whilst  two  pipes  collapsed  owing  to  failure  of  designers 
to  provide  plates  whose  unit  stress  should  be  suitable  for  con- 
ditions well  recognized  at  this  date.  Deducting  those  pipes 
whose  partial  or  total  destruction  should  have  been  provided 
against,  there  remains  only  four  failures  unexplained,  and  one 
of  these  might  be  placed  if  the  history  of  the  structure  were 
known. 

In  view  of  this  testimony  and  the  most  conclusive  and 
practical  evidence  offered  by  the  constant  and  increasing  use 
of  structural  steel,  there  can  be  no  question  as  to  the  fitness 
and  adaptability  of  this  product  to  the  many  purposes  of  the 
mechanical  arts. 

Continuing  the  consideration  of  this  question,  an  interest- 
ing discussion  upon  the  choice  of  materials  may  be  found 
in  Prof.  W.  D.  Pence's  "Stand-pipe  Accidents  and  Fail- 
ures," which,  on  account  of  its  clearness  and  propriety,  is  pre- 
sented here  literally : 

"Relative  Merits. — In  weighing  the  relative  merits  of 
steel  and  wrought  iron  as  materials  for  the  construction  of 
stand-pipes,  it  may  not  be  denied  that  each  material  has  points 
of  excellence  possessed  either  in  a  less  degree,  or  perhaps  not 
at  all,  by  the  other.  Judging  alone  from  the  recorded  failures 
of  the  two  metals  in  actual  service,  wrought  iron  appears 
preferable  to  steel.  However,  an  entirely  just  interpretation 
of  this  record  must  recognize  the  fact  that  a  majority  of  the 
total  failures  of  steel  stand-pipes  may  be  traced  to  the  use  of 
ill-adapted  or  exceptionally  inferior  grades  of  that  metal. 
With  this  qualification,  the  contrast  in  the  records  of  the  two 
materials  is  much  reduced,  if  indeed  it  is  not  quite  elimin- 
ated. Careful  consideration  of  the  foregoing  records  and 
facts  related  thereto  leads  to  the  following  conclusions : 

"(i)  That  steel  plate  of  cheap  grades  is  certainly  a 
dangerous  material  to  use  in  the  construction  of  stand-pipes. 


V      OF   THE 

UNIVERSITY 

OF 


USE    OF  IRON.  53 


"(2)  That  steel  plate  of  proper  quality  is  a  safe  material 
for  the  construction  of  stand-pipes. 

"(3)  That  wrought-iron  plate,  equivalent  in  quality  to  the 
usual  grades  of  that  material  hitherto  employed  for  stand- 
pipe  construction,  is  a  safe  material  for  this  purpose. 

"  The  first  of  these  conclusions  is  substantiated  by  a  num- 
ber of  the  more  widely  known  failures  of  steel  stand-pipes.  The 
second  is  warranted  by  the  scarcity  of  failures  of  steel  stand- 
pipes,  in  whose  construction  proper  grades  of  plate  metal 
were  used.  The  truth  of  the  third  is  evidenced  by  the  sev- 
eral classifications  of  accidents  and  failures. 

"The  decided  preference  for  steel,  which  has  grown  so 
rapidly  in  other  fields  of  work,  applies  with  full  force  in  the 
construction  of  stand-pipes,  and  it  has  now  reached  such  a 
stage  that  exceedingly  few  concerns  make  a  specialty  of 
building  wrought-iron  stand-pipes.  An  important  result  of 
this  evolution,  which  in  the  future  may  require  a  qualification 
of  the  third  conclusion  above  stated,  is  thus  described  by  a 
recognized  authority  in  the  field  of  structural  tests:  'Steel 
for  most  structural  purposes  has  so  far  replaced  wrought  iron 
that  it  is  now  difficult  to  get  competition  among  the  manu- 
facturers of  wrought  iron  for  structural  purposes.  Many  of 
the  manufacturers  who  are  still  making  wrought  iron  find  that 
the  demand  is  so  much  greater  for  steel — and  in  fact  the  profit 
better  in  steel — that  they  are  not  putting  the  care  and  atten- 
tion to  the  manufacture  of  wrought  iron  that  they  have  in  the 
past,  and  it  is  getting  every  month  harder  and  harder  to  ob- 
tain the  best  grades  of  wrought  iron  for  structural  purposes. 
There  are,  however,  still  a  few  concerns  who  are  holding  up 
their  reputations  and  manufacturing  as  good  wrought  iron  as 
in  the  past.' ' 

Another  authority  in  the  same  field  expresses  the  opinion 
that:  "  The  quality  of  wrought  iron  is  about  the  same  as  it 
was  before  the  *  era  of  steel/  but  engineers  and  inspectors 


54  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

who  have  to  deal  with  materials  for  structural  purposes  are  no 
longer  as  familiar  with  iron  as  they  were  some  time  ago,  or 
a?  they  are  with  steel." 

In  view  of  the  conflict  of  opinion  indicated  by  the  ex- 
pressions above  quoted,  particular  interest  attaches  to  the  fol- 
lowing statement  from  a  well-known  firm  of  boiler-merchants, 
having  an  experience  covering  a  period  of  more  than  half  a 
century: 

"  There  are  very  few  mills  to-day  that  have  among  their 
employees  men  who  can  make  first-class  iron,  and  by  reason 
of  the  fact  that  orders  for  iron  are  so  exceedingly  rare  and 
these  men  can  be  put  at  the  work  only  at  infrequent  inter- 
vals, their  skill  has  departed  and  they  have  no  longer  the 
ability  to  make  as  good  iron  as  was  made  five  or  ten  years 
ago. 

"Whatever  the  present  status  of  the  question,  it  is  perti- 
nent to  observe  that  the  results  of  a  very  similar  rivalry  be- 
tween steel  and  wrought  iron  in  the  manufacture  of  T  rails, 
some  years  ago,  tends  forcibly  to  confirm  the  belief  that  the 
quality  of  the  superseded  metal  must  decline  sooner  or  later 
in  the  case  under  consideration.  Such  deterioration  having 
taken  place,  it  seems  quite  certain  that  wrought  iron  could  show 
no  superiority  over  steel  in  open  competition,  and,  as  re- 
marked in  discussing  this  subject  at  the  conclusion  of  the 
original  record  of  accidents,  it  seems  altogether  probable 
that  the  favorable  showing  of  wrought  iron  indicated  by  the 
record  of  stand-pipe  failures  would  soon  be  forfeited  were  the 
extensive  use  of  wrought  iron  for  this  purpose  to  be  suddenly 
resumed  without  a  corresponding  restoration  of  the  former 
qualities  of  that  metal.  Fortunately,  the  few  firms  that  have 
adhered  loyally  to  the  use  of  wrought-iron  and  have  built 
most  of  the  large  wrought-iron  stand-pipes  during  the  period 
of  alleged  retrogression,  seem  to  have  recognized  the  impor- 


THE    USE    OF  IRON.  55 

tance  of  using  good  grades  of  that  metal,  so  that  the  decline 
in  safety,  above  suggested,  has  probably  not  begun. 

"  Very  naturally  the  reduced  cost  of  steel,  attended  by  a 
growing  confidence  in  its  uniformity  and  high  quality  when 
demanded,  has  led  to  a  decided  preference  for  that  metal. 
That  this  preference  will  not  be  modified  under  present  con- 
ditions seems  very  certain,  but  this  fact  will  not,  and  very 
properly  should  not,  prevent  the  use  of  wrought  iron  of  ap- 
propriate grades  when  preferred.  Since  little  assurance  of 
excellence  is  to  be  found  in  the  mere  names  steel  or  wrought 
iron,  the  really  vital  consideration  is  not  so  much  which  metal 
as  what  grade  of  the  chosen  metal." 

Upon  a  subject  where  there  is  room  for  so  wide  an  expres- 
sion of  individual  opinion,  and  in  view  of  the  conservative  ten- 
dency which  bids  the  manufacturer  as  well  as  the  engineer 
"  Be  not  the  first  by  whom  the  new  is  tried,"  there  is  little 
wonder  at  the  following  expression  from  one  of  the  most 
long-established  and  eminently  reliable  and  respectable  metal 
workers  upon  the  use  of  steel  or  iron  plate  in  stand-pipe  con- 
struction : 

"  We  do  consider  iron  plates  more  uniform  in  composition 
and  better  adapted  for  stand-pipe  construction,  regardless  of 
question  of  cost,  than  steel  plates  of  the  standard  chemical 
and  physical  properties,  as  we  are  able  to  obtain  those  plates. 
The  difficulty  the  mills  rolling  plates  meet  with  is  that  they 
can  not  produce  all  plates  of  the  quality  they  desire. 

"  Our  specifications  for  a  stand-pipe  iron  plate  are  merely 
that  the  plate  shall  be  double  refined  and  fibrous  in  nature,  not 
crystallized  in  its  composition,  48,000  to  $0,000  pounds  ten- 
sile strength,  and  made  from  such  mixture  of  pig  iron  as  we 
know  will  unite  in  making  a  strong  plate.  We  have  used  one 
mixture  of  pig  iron,  comprising  three  different  grades  of  pig, 
for  a  period  of  twenty  years  in  stand-pipe  plates,  and  there 
never  has  been  a  failure  of  one  plate  of  this  material.  It 


56  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

may  be  an  interesting  fact  for  you  to  know  that  every  stand- 
pipe  which  has  mysteriously  broken  or  burst,  has  been  built 
of  steel  plates.  (Statement  not  substantiated  by  facts.) 

"  We  have  no  specifications  of  our  own  for  steel  plates,  but 
have  adopted  in  our  use  either  the  specifications  adopted 
as  standard  by  the  American  Rolling  Mill  Association,  or 
the  specifications  adopted  by  the  American  Boiler  Makers' 
Association,  either  of  which  we  regard  as  good  as  can  be 
obtained.  .  .  .  We  would  hesitate  very  much  before  using  steel 
rivets  in  stand-pipe  work-.  While  the  steel  makers  have 
made  great  progress  and  improved  very  much  in  the  manufac- 
ture of  steel  plate,  they  have  not  met  with  equal  success  in 
manufacturing  a  rivet  steel. 

"  The  difference  between  the  United  States  Naval  Depart- 
ment and  the  Carnegie  Company  in  reference  to  ship-plates 
made  for  the  department,  and  to  be  used  at  Newport  News, 
is  a  fair  illustration  of  the  inability  of  plate  makers  to  make  a 
uniform,  homogeneous  grade  of  steel  plate  in  every  case.  If 
you  read  up  in  the  matter,  you  will  recall  that  the  plates  were 
made  under  strict  specifications  as  to  the  physical  and  chem- 
ical requirements,  and  that  every  stage  in  the  process  of  their 
manufacture  was  watched  by  experts,  both  on  the  part  of  the 
Government  and  on  the  part  of  the  manufacturer,  and  yet 
when  the  plates  were  finished  and  shipped  to  Newport  News, 
the  ship-builders  and  the  experts  watching  the  construction 
of  the  work,  discovered  that  many  plates  cracked.  The 
matter  was  referred  to  a  commission  and  it  was  agreed  that 
in  view  of  all  the  facts,  and  allowing  for  the  inability  to 
control  the  product  of  a  steel  mill,  the  Government  could  not 
condemn  all  the  plates  delivered,  neither  could  they  accept 
all,  but  that  the  use  of  plates  would  depend  entirely  upon  the 
result  of  the  shop- work  at  Newport  News." 

The  foregoing  having  to  do  principally  with  the  relative 
utility  of  the  two  metals  and  regardless  of  commercial  con- 


THE    USE    OF  IRON.  57 

siderations,  and  as  these  last  are  governing  factors  in  this 
practical  age,  a  comparison  is  certainly  not  complete  without 
considering  market  values  or  intrinsic  worth  of  the  two  metals. 

One  of  a  set  of  specifications  calling  for  proposals  for 
wrought-iron  stand-pipe  construction  was  issued  in  October, 
1897,  the  dimensions  of  the  pipe  being  15  ft.  by  1 10  ft., 
the  metal  to  conform  to  the  following  requirements : 

"  The  material  of  which  the  stand-pipe  shall  be  built  shall 
be  a  good,  sound,  rolled  plate,  having  a  tensile  strength  of  not 
less  than  forty-eight  (48,000)  thousand  pounds  per  square 
inch  of  section ;  elastic  limit,  twenty-four  (24,000)  thousand 
pounds;  elongation  not  less  than  15^  in  a  full  section  of  test- 
piece  8  in.  long,  and  on  examination  show  no  sign  of  inferior 
workmanship.  Each  plate  shall  be  stamped  with  the  name 
of  the  manufacturer  and  its  tensile  strength."  The  shop  to 
whom  the  award  was  made  furnished  at  the  same  time  an  al- 
ternate proposal  for  steel  plate  under  the  following  manufac- 
turers' guarantee : 

Steel  plate  T3F  in.  to  £in.  T.  S.  60,000  to  66,000  Ibs.  persq.  in. 
"      i-    "     <<T^«    T.  S.  54,000"  58,000  "     "     "   " 
"     T8T  "     "f"    T.  S.  56,000  "  60,000   "     li    "   " 
"        "     j\  "   and  upward     58,000  "  64,000   "      "     "   " 
Elastic  limit  more  than  J-  T.   S. 
Elongation,  8  in.  section  (at  least),  20$  for  all  plates  overf  in. 

thick. 
Reduction  of  area,  at  least  50$. 

The  market  prices  of  the  two  metals  at  the  date  of  these 
proposals  were  as  follows  f.  o.  b.  cars  at  mills : 
Steel  plate,  $1.05  per  loolbs. 
Iron    plate  $1.40     "      "      " 
Iron  rivets  50  cts.  per  100  more  than  steel. 

The  estimated  weights  of  the  stand-pipe  material  were  as 
follows : 


$8  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

For  iron,  weight  of  plates  and  angles  81,600  Ibs. 
For  steel,  weight  of  plates  and  angles  85,680  Ibs. 

[NOTE. — Increased  weight  approximates  an  additional  weight  of  5$ 
of  steel  over  iron  of  like  dimensions.] 

Estimated  amount  of   rivets,  4,600  Ibs.,   including   waste  al- 
lowance. 

The  estimated  cost  of  the  superstructure,  therefore,  would 
be  as  follows : 

81,600  Ibs.  iron  plates  at  $1.40 $i  142.40 

85,680  Ibs.  steel  plates  "     1.05 899.64 


Difference  in  favor  of  steel $  242.76 

A  comparison  of  the  relative  tensile  strength  of  the  two 
metals  shows  an  advantage  of  about  22#  in  favor  of  steel,  and 
had  steel  plate  been  selected,  allowing  for  the  increase  of 
strength,  the  thickness  might  have  been  so  reduced  as  to  have 
permitted  a  reduction  of  18,850  Ibs.,  at  the  market  price, 
effecting  a  further  saving  of  $197.92,  or  a  total  saving  of 
$440.68  had  steel  plate  instead  of  wrought  iron  been  used. 

Comparative  Cost. — In  citing  this  particular  I45,ooo-gal. 
stand-pipe  for  the  purpose  of  arriving  at  conclusions  as  to  rela- 
tive cost  of  two  possible  metals,  it  may  be  urged  that  a  higher 
grade  of  steel  should  have  been  insisted  upon  in  order  to  make 
the  comparison  possible  ;  however  this  may  be,  there  can  be  no 
controversion  of  the  fact  that  in  equivalent  metals  the  greater 
strength  in  proportion  to  volume  and  weight,  gives  steel  a 
clear  preference  of  something  like  2O#  as  applied  to  ruling 
prices.  Such  reasons  have  led  to  an  almost  universal  demand 
for  steel  as  a  structural  metal,  and  its  choice  may  be  conceded. 
This  preference  having  been  allowed,  the  particular  grade  of 
steel  best  adapted  to  constructive  purposes  must  receive  con- 
sideration. 

It  has  been  explained  that  structural  steel  is  the  product 


THE    USE    OF  IKON.  59 

of  two  processes,  the  Bessemer  and  open-hearth,  either  acid 
or  basic. 

At  present  there  are  no  limitations  fixed  by  the  manufac- 
turers' standard  specifications  in  the  matter  of  process  of 
manufacture,  one  of  the  initial  clauses  of  these  specifications 
being  "  Steel  may  be  made  by  either  the  open-hearth  or  Bes- 
semer process,"  and  no  notice  of  the  further  refinement  possibly 
resulting  from  the  character  of  the  furnace-lining  is  taken; 
notwithstanding  this,  each  process  of  manufacture  has  its 
ardent  advocates. 

Comparative  Homogeneity  and  Strength  of  Bessemer  and 
Open-hearth  Steels. — The  Bessemer  or  converter  process 
attaining  its  highest  commercial  development  when  operating 
upon  a  grand  scale  and  in  supplying  an  immense  output,  it  is 
questionable  whether  such  conditions  are  as  favorable  for 
scientific  and  exact  production  of  steel  as  the  less  extensive 
furnace  or  open-hearth  system,  and  where,  at  any  period  of 
evolution,  tests  may  be  made  with  regularity  and  certainty, 
and  the  process  discontinued  at  the  precise  moment  deemed 
most  suitable. 

In  addition  to  the  requirements  of  the  manufacturers'  stand- 
ard specifications,  the  American  Boiler  Association  demands 
"  homogeneous  "  metal.  If  the  initial  metal  is  low  in  phos- 
phorus and  sulphur,  the  finished  product  may  be  sufficiently 
uniform  for  all  practical  purposes,  but  entire  and  absolute 
homogeneity  and  absence  of  segregation  is  at  this  time  unat- 
tainable, but  from  the  fact  that  in  the  acid  open-hearth  pro- 
cess the  phosphoric  and  sulphuric  components  of  the  charge 
remain  unaffected  during  the  process  of  evolution,  it  is  pos- 
sible that  this  system  of  manufacture  should  be  given  a  prefer- 
ence. This  reasoning  applies  with  equal  force  to  the  favor 
shown  by  some  engineers  toward  the  acid  rather  than  the 
basic  method  of  production,  a  definite  allowance  of  some  two 
or  three  per  cent,  sometimes  being  permitted,  the  idea  being 


60  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

that  assurance  shall  be  made  doubly  sure.  It  would  seem  that 
if  this  difference  is  to  be  recognized,  the  acid  metal  should 
alone  be  considered,  except  at  a  different  commercial  value, 
in  the  choice  of  structural  steel.  It  is  interesting  to  note, 
however,  that  the  British  Royal  Navy  has  endorsed  the  fol- 
lowing report :  "With  converter  steel,  riveted  samples  have 
given  less  average  strength,  greater  variation  in  strength,  and 
much  more  irregularity  in  modes  of  fracture  than  similar  sam- 
ples of  open-hearth  steel.  The  basic  open-hearth  metal  has 
proven  to  be  as  good  as  that  made  on  the  acid  hearth,  and 
after  full  investigation,  it  will  be  used  by  the  Admiralty  in 
ship  plates  and  boiler  tubes  on  an  equal  footing." 

In  "  Manufacture  and  Properties  of  Structural  Steel," 
the  author  has  this  to  say  of  the  two  processes  of  steel  making : 
"  My  own  experience  leads  me  to  think  that  Bessemer  steel 
requires  more  work  for  the  attainment  of  a  proper  structure 
than  open-hearth  metal,  so  that  a  thick  bar  is  more  apt  to 
have  a  coarse  crystalline  fracture.  This  may  be  ascribed  in 
any  particular  case  to  improper  treatment,  but  if  it  is  true  that 
open-hearth  metal  would  not  be  injured  under  a  similar  ex- 
posure, then  it  is  proven  that  there  is  a  difference  between 
the  metals,  and  if  this  be  acknowledged,  then  there  is  no 
necessity  for  further  argument. 

"  It  is  true  that  Bessemer  metal  has  been  used  for  rails,  and 
that  these  are  exposed  to  great  stress  and  shock,  but  it  is  also 
true  that  a  large  number  of  rails  break  in  service,  and  that  the 
use  of  ordinary  steel  rail  for  bridges  was  long  ago  given  up  as 
dangerous.  Moreover  it  is  quite  probable  that  the  number  of 
broken  rails  would  be  considerably  reduced  if  they  were  made 
of  open-hearth  steel.  It  is  acknowledged  that  the  case  is  not 
yet  closed,  but  until  the  foregoing  statements  are  controvert- 
ed by  direct  and  positive  evidence,  the  only  safe  way  for  the 
engineer  is  to  prescribe  that  only  open-hearth  metal  shall  be 
used  in  all  structures  like  railroad-bridges,  where  the  steel  is 


THE    USE   OF  IRON.  6 1 

under  constant  shock,  and  where  life  and  death  are  in  the  bal- 
ance. In  this  connection  it  should  be  stated  that  the  method 
by  which  the  steel  is  made  cannot  be  discovered  by  ordinary 
chemical  analysis.  Certain  experiments  indicate  that  there  is 
a  difference  between  Bessemer  and  open-hearth  steel  in  the 
character  of  the  occluded  gases,  but  this  system  of  analysis  is 
never  resorted  to  in  practice,  and  no  provision  is  made  for  it 
in  laboratories.  Moreover  it  is  doubtful  if  any  expert  would 
risk  his  reputation  by  asserting  positively,  from  any  such  evi- 
dence, that  a  certain  steel  was  made  by  either  one  or  the 
other  process.  Consequently,  when  open-hearth  metal  is 
specified,  a  careful  watch  should  be  kept  in  the  steel-works 
that  there  is  no  substitution  of  the  inferior  metal." 

Many  such  honest  but  possibly  biased  arguments,  contro- 
verting Mr.  Campbell's  opinions,  might  be  inserted,  but  the 
tendency  would  be  to  lead  us  back  to  our  starting-point,  and 
it  is  possibly  best  to  conclude  with  the  following  clear  and  un- 
prejudiced, if  not  entirely  scientific,  statement  of  the  case  by  a 
reputable  trades  journal : 

Suitable  Grades  for  Structural  Work. — "The  terms  '  Bes- 
semer '  and  '  open-hearth  '  steels  have  reference  to  methods 
or  processes,  and  not  necessarily  to  qualities.  If  a  good  qual- 
ity of  pig  iron  is  made  into  steel  by  either  the  Bessemer  or 
open-hearth  process,  it  would  be  found  that  the  latter  was 
softer  and  more  uniform  under  the  stress  of  severe  usage. 
But  Bessemer  steel  made  of  good  iron  is  better  than  open- 
hearth  steel  made  of  a  cheap  and  inferior  material.  There- 
fore the  Bessemer  'tank'  steel  of  some  manufacturers  will 
run  better  than  the  open-hearth  '  flange '  steel  of  other 
makers.  The  name  don't  make  the  quality." 

The  preponderence  of  testimony  and  evidence  seems  to 
point  to  open-hearth  metal  as  preferable  for  stand-pipe  con- 
struction, but  after  having  specified  this,  it  is  of  the  utmost  im- 
portance to  see,  not  only  that  it  is  furnished,  but  that  the  char- 


62  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

acter  of  the  finished  product  is  of  a  suitable  grade,  whose 
chemical  and  physical  properties  having  been  specified,  will  be 
conscientiously  made  to  meet  the  requirements.  This  ad- 
vances two  important  subjects:  first,  What  chemical  and  phys- 
ical requirements  are  deemed  most  suitable  for  stand-pipe 
work  ?  and,  having  determined  this,  How  can  certainty  in  ob- 
taining what  is  considered  requisite  be  secured  ? 

The  temperature  at  which  steel  is  finished,  depending  ob- 
viously upon  the  mass  being  worked,  has  been  shown  to  exert 
a  marked  effect  upon  its  physical  properties,  and  to  such  an 
extent  that  concessions  are  allowed  amounting,  as  will  be 
observed  from  the  manufacturers'  standard,  to  10,000  pounds 
to  cover  the  various  widths  and  thicknesses  of  sections.  There 
seems  to  be  an  increasing  tendency  to  test  each  separate  thick- 
ness, and  in  view  of  the  fact  that  tests  made  from  the  same 
melt  but  upon  different  thicknesses  of  metal,  finished  at  differ- 
ent temperatures  show  great  variability  in  tensile  strength, 
the  practice  seems  commendable.  Considering  the  physical 
characteristics  of  a  good  structural  steel,  authorities  agree  that 
the  metal  should  be  soft,  tough,  and  ductile ;  disputing,  how- 
ever, as  to  the  exact  limits  and  variation  in  tensile  strength. 
In  this  connection  Mr.  Campbell  says: 

4 'The  tendency  in  the  first  epoch  of  steel  structures  was 
toward  a  hard  alloy,  but  the  later  practice  has  been  a  con- 
tinual progress  toward  toughness.  There  was  a  halt  in  this 
movement  at  a  tensile  strength  of  60,000  pounds,  not  entirely 
on  account  of  any  magic  virtue  in  the  figure,  but  because  the 
ordinary  mild  steels  gave  that  result,  and  a  much  higher  price 
was  charged  for  a  softer  metal.  The  conditions  to-day  are 
bomewhat  different,  for  the  reduced  cost  of  low-phosphorus 
pig  iron,  and  the  introduction  of  the  basic-hearth,  have  alter- 
ed the  economic  situation. 

"A  steel  with  a  tensile  strength  of  50,000  to  58,000 
pounds  per  square  inch  is  a  most  attractive  material,  possess- 


THE    USE   OF  IRON.  63 

ing  all  the  good  characteristics  of  wrought  iron,  with  greater 
strength  and  toughness,  and  it  seems  probable  that  it  will  be 
extensively  used  in  the  future." 

According  to  Campbell,  the  German  specifications  in  most 
general  use  call  for  the  following  physical  conditions: 

"For  rivets:  Ultimate  strength  from  51,200  to  59,700 
pounds  per  square  inch;  elongation,  22  per  cent,  in  eight 
inches. 

* '  For  other  structural  material :  Lengthwise  tests,  ultimate 
strength  from  52,600  to  62,600  pounds  per  square  inch;  elon- 
gation, 20  per  cent,  in  eight  inches. 

"Crosswise  tests:  Ultimate  strength  from  51,200  to 
64,000  pounds  per  square  inch;  elongation,  17  per  cent,  in 
eight  inches." 

Commenting  upon  these  requirements,  Mr.  Campbell  says  : 
"It  is  safe  to  say  that  if  American  engineers  were  satisfied 
with  the  German  standards,  there  would  not  be  one  rejection 
for  deficient  ductility  where  there  are  twenty  under  our  more 
rigid  requirements;  and  if  they  would  be  content  with  a  steel 
having  an  ultimate  strength  between  52,000  and  62,000 
pounds  per  square  inch,  there  would  not  be  one-fifth  the 
number  of  heats  discarded  for  being  outside  of  the  tensile 
limits.  The  bearing  of  these  facts  upon  the  cost  of  the  ma- 
terial is  self-evident. 

"  I  do  not  advocate  any  sacrifice  of  strength  to  economy, 
but  I  would  impress  upon  the  American  engineers  that  this 
soft  metal  is  eminently  suited  to  structural  work,  while  by 
maintaining  their  present  chemical  limitations  and  their  re- 
quirements concerning  ductility,  they  will  be  assured  of  a 
material  which  is  equal  in  quality  to  any  produced  in  the 
world." 

In  a  recent  publication,  one  of  the  largest  manufacturers 
of  structural  steel  records  his  conclusions  as  follows: 

"The  strength  of  structural  steel  depends  largely  on  the 


64  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

amount  of  the  constituent  elements  that  are  associated  with 
the  iron,  and  each  of  which  affect  more  or  less  the  hardness 
and  strength  of  the  material. 

"The  principal  of  these  are  carbon,  manganese,  silicon, 
phosphorus,  and  sulphur,  the  first-named  being  purposely 
retained  as  useful  or  necessary,  the  others  being  rejected,  as 
far  as  practicable,  as  objectionable  when  in  excess  of  certain 
minute  proportions. 

"  The  grade  and  character  of  the  steel  is  usually  known  by 
the  percentage  of  contained  carbon.  Steel  used  in  structures 
usually  varies  in  tensile  strength  from  55,000  to  70,000  Ibs. 
per  square  inch  of  section,  or  from  .10  to  .25  per  cent,  of 
carbon. 

"  The  following  table  exhibits  the  physical  characteristics 
of  open-hearth  basic  steel  of  the  various  grades,  the  results 
derived  from  an  extensive  series  of  tests  indicating  the  ten- 
dency of  a  total  average  of  the  composition  hereafter  de- 
scribed to  approximate  to  the  figures  given  in  the  table. 

"The  predominant  elements  other  than  carbon  averaged 
throughout  the  series  as  follows  :  manganese,  .40 ;  phosphorus, 
.04;  sulphur,  .05  percent.  Any  increase  of  these  elements 
is  attended  with  an  increase  of  tensile  strength  and  reduced 
ductility,  and  vice  versa.  The  tensile  strength  of  the  steel 
is  also  affected  to  some  extent  by  the  temperature  at  which  it 
is  finished,  and  the  rate  of  cooling;  these  influences  being 
more  apparent  in  the  grades  containing  highest  carbon. 
Therefore  the  values  given  have  only  a  general  significance, 
and  the  results  of  individual  tests  may  vary  widely  above  or 
below  the  figures  in  the  table. 

"  For  Bessemer  or  open-hearth  acid  process  steel,  the  ten- 
sile strength  will  ordinarily  be  greater  for  the  same  percent- 
age of  carbon  given  in  this  table,  for  the  reason  that  the  pro- 
portions of  phosphorus  and  sulphur,  and  sometimes  manga- 
nese, are  usually  higher  than  in  open-hearth  basic  steel,  each 


THE    USE   OF  IRON. 


of  these  elements  contributing  to  strength  and  hardness  in 
the  steel." 

OPEN-HEARTH  BASIC  STEEL. 


Percentage 
of 
Carbon. 

Tensile  Strength  in  Pounds  per  sq.  in. 

Ductility. 

Ultimate  Strength. 

Elastic  Limit. 

Stretch  in  8  inches. 

Reduction  of 
Fractured  Area, 

.08 

54,000 

32,500 

32  per  cent. 

60  per  cent. 

.09 

54,800 

33,000 

3i 

58 

.IO 

55.700 

33-500 

3i 

57 

.11 

56,500 

34.000 

30 

56 

.12 

57,400 

34.500 

30 

55 

•13 

58,200 

35,000 

29 

54 

.14 

59.10° 

35,500 

29 

53 

•15 

60,000 

36,000 

28 

52 

.16 

60,800 

36,500 

28 

5i 

•17 

61,600 

37,000 

27 

50 

.j.8 

62,500 

37,500 

27 

49 

.19 

63,300 

38,000 

26 

48 

.20 

64,200 

38,500 

26 

47 

.21 

65,000 

39,000 

25 

46 

.22 

65,800 

39,500 

25 

45 

•23 

66,600 

40,000 

24 

44 

.24 

67,400 

40,500 

24 

43 

.25 

68,200 

41,000 

23 

42 

"Distinguishing  Terms. — For  convenient  distinguishing 
terms,  it  is  customary  to  classify  steel  in  three  grades ;  *  mild  or 
soft,'  '  medium/  and  '  hard,'  and  although  the  several  grades 
blend  into  each  other,  so  that  no  line  of  distinction  exists,  in 
a  general  sense  the  grades  below  .15  per  cent,  carbon  may  be 
considered  as  '  soft '  steel;  from  .  15  to  .30  per  cent,  carbon  as 
*  medium  ' ;  and  above  that,  '  hard  '  steel.  Each  grade  has  its 
own  advantages  for  the  particular  purpose  to  which  it  is 
adapted.  The  soft  steel  is  well  adapted  for  boiler-plate  and 
similar  uses,  where  its  high  ductility  is  advantageous.  The 
medium  grades  are  used  for  general  structural  purposes,  while 
harder  steel  is  especially  adapted  for  axles  and  shafts,  and 


66  TOWERS   AND    TANKS  FOR    WATER-WORKS. 

any  service  where  good  wearing  surfaces  are  desired.  Mild 
steel  has  superior  welding  properties  as  compared  with  hard 
steel,  and  will  endure  higher  heat  without  injury.  Steel 
below  .10  per  cent,  carbon  should  be  capable  of  doubling 
flat  without  fracture  after  being  chilled  from  a  red  heat  in  cold 
water.  Steel  of  .  i  5  per  cent,  carbon  will  occasionally  submit  to 
the  same  treatment,  but  will  usually  bend  around  a  curve 
whose  radius  is  equal  to  the  thickness  of  the  specimen ; 
about  90  per  cent,  of  specimens  stand  the  latter  bending- 
test  without  fracture.  As  the  steel  becomes  harder,  its 
ability  to  endure  this  bending-test  becomes  more  exceptional, 
and  when  the  carbon  ratio  becomes  .20  per  cent.,  little  over 
25  per  cent,  of  specimens  will  stand  the  last-described  bend- 
ing-test.  Steel  having  about  .40  per  cent,  carbon  will  usually 
harden  sufficiently  to  cut  soft  iron  and  maintain  an  edge." 

The  classification  of  steel  seems  to  the  average  layman  a 
little  arbitrary.  As  shown  in  the  preceding  quotation,  "  For 
convenient  distinguishing  terms,  it  is  customary  to  classify 
steel  in  three  grades,  etc."  The  classification  according  to 
the  manufacturers'  standard  specifications  is  that  "  Steel  shall 
be  of  four  grades:  '  extra  soft,'  '  fire-box,'  '  flange  or  boiler,' 
and  '  boiler-rivet  '  steel.  Commercially,  and  as  quoted  in  the 
trades  papers,  the  classification  is  as  follows:  'tank,'  'shell,' 
'  flange,'  '  ordinary  fire-box,'  and  '  locomotive  fire-box.'  ' 

In  reply  to  an  inquiry  as  to  the  average  physical  and 
chemical  properties  of  each  of  the  commercial  grades,  one  of 
the  largest  testing-laboratories  in  the  United  States  writes  as 
follows:  "While  we,  of  course,  keep  records  of  all  tests 
made  by  us,  they  are  not  tabulated  nor  averaged.  We 
doubtless  have  on  record  several  hundred  thousand  tests  of 
all  grades  of  material  made  from  nearly  all  the  different  steel 
works  in  the  country.  We  can,  however,  give  you  approxi- 
mately what  the  different  grades  of  steel  run,  as  follows: 


THE    USE   OF  IRON.  6? 

"  MEDIUM   STEEL   (TANK). 

Tensile  strength 60,000  to  68,000  Ibs.  per  sq.  in. 

Elastic  limit,  one-half  the  ultimate  strength. 

Elongation . . 20  to  23$ 

Reduction  of  area 40  "  45$ 

Chemical   requirements  for   phosphorus  and   sulphur  same  as  for 
"  soft  steel." 

"  SOFT    STEEL    (SHELL). 

Tensile  strength 54,000  to  62,000  Ibs.  per  sq.  in- 

Elastic  limit,  one-half  the  ultimate  strength. 

Elongation 25$ 

Reduction  of  area 50$ 

If  acid  open-hearth  steel  :  phosphorus  under 085$ 

"        sulphur  under 065^ 

If  basic  open-heath  steel :  phosphorus  under 035$ 

"        sulphur  under .04$ 

"  FLANGE   STEEL. 

Ultimate  tensile  strength 54,000  to     62,000  Ibs.  per  sq.  in. 

Elastic  limit,  not  less  than 33,000  Ibs. 

Elongation 27% 

Reduction  of  area 50$ 

If  acid  open-hearth  steel : 

Phosphorus  not  more  than .065$ 

Sulphur  not  more  than 05$ 

jf  basic  open-hearth  steel : 

Phosphorus  not  more  than 035$ 

Sulphur  not  more  than    035$ 

"  FIRE-BOX   STEEL. 

"  To  be  made  of  acid  open-hearth  steel  of  the  following  strength  : 

UUimate  tensile  strength 56,000  to    64,000  Ibs.  per  sq.  in. 

Elastic  limit 33,000  Ibs. 

Elongation ,. 28$ 

Reduction  of  area.. , . ,  t 56$ 

Phosphorus 035$ 

Sulphur , ., , 03  5# 


68  TOWERS  AND    1 'ANA'S  FOR    WATER-WORKS. 

"  LOCOMOTIVE    FIRE-BOX   STEEL. 
[NOTE. — Specifications  of  Baldwin  Locomotive  Works.] 

Tensile  strength,  55,000  1065,000  Ibs.  per  sq.  in. 
Elongation,  20  to  25  per  cent. 
Carbon,  .15  to  .25  per  cent. 
Phosphorus,  not  over  .03  per  cent. 
Manganese,  not  over  .45  per  cent. 
Silicon,  not  over  .03  per  cent. 
Sulphur,  not  over  .035  per  cent. 
All  plate  to  be  manufactured  by  the  open-hearth  process. 

"RIVET    STEEL. 

Tensile  strength" , 50,000  to  60,000  Ibs.  per  sq.  in. 

Elastic  limit,  one-half  the  ultimate  strength. 

Elongation 25  to  28$ 

Reduction  of  area 50  to  55$ 

If  acid  open-hearth  steel : 

Phosphorus  not  more  than .075$ 

Sulphur  not  more  than .06$ 

If  basic  open -hearth  steel  : 

Phosphorus  not  more  than .035$ 

Sulphur  not  more  than ; .04$ 

"  BOILER-RIVET   STEEL. 

"  Same  as  rivet  steel,  except  that  a  lower  percentage  of  sulphur  and 
phosphorus  should  be  asked  for,  and  also  a  slightly  greater  elongation 
and  reduction." 

Owing  to  the  comparatively  small  quantities  of  rivets  re- 
quired in  stand-pipe  construction,  tests  for  rivet-rod  metal 
are  hardly  practicable,  and  therefore  specifications  governing 
same  being  useless,  it  would  seem  that  the  practical  method 
of  securing  a  suitable  grade  of  rivet  metal  is  to  purchase  by 
the  keg  of  manufacturers  who  have  a  standing  reputation  as 
rivet  makers,  and  for  this  certain  field-tests  should  be  re- 
quired. 

Specifications. — In  discussing  the  suitability  of  the  several 
grades  of  steel  for  stand-pipe  construction  work,  Prof.  Pence 


THE    USE    OF  IRON. 


69 


has  this  to  say :  "  The  usual  market  grades  of  steel  plate  may 
be  described  as  follows :  Tank  steel  is  the  cheapest  grade. 
Its  low  price  is  due  primarily  to  the  grade  of  stock  used, 
giving  a  metal  with  high  percentages  of  the  detrimental 
elements,  even  without  the  careless  manipulation  which  cheap 
work  is  so  apt  to  receive.  The  quality  of  the  tank  steel  pro- 
duced by  a  few  makers  is  sometimes  quite  good,  but  experi- 
ence has  shown  it  to  lack  uniformity,  and  good  authorities 
generally  agree  in  condemning  its  use  in  important  structures. 
While  it  may  display  the  physical  excellence  of  the  best 
grades  of  steel,  *  it  is  apt  to  be  hard  and  brittle,  and  should 
never  be  used  in  any  part  of  a  stand-pipe/  It  is  believed 
by  some  that  a  fruitful  cause  for  the  treachery  of  tank  steel  is 
to  be  found  in  the  practice  of  selling  under  that  classification 
steel  plate  which  has  been  rejected  from  higher  grades.  It 
is  common  to  find  merely  the  tensile  strength  of  this  grade  of 
steel  specified,  '60,000  T.  S.'  being  the  usual  requirement. 

11  Shell  steel  is  the  next  better  grade.  Its  greater  excel- 
lence and  enhanced  cost  are  due  to  the  use  of  more  care  in 
selecting  the  stock  and  in  perfecting  the  chemical  nature  of 
the  finished  product.  Shell  steel  is  used  in  ordinary  boiler- 
construction,  and  many  stand-pipes  have  been  built  from  it. 
It  is,  of  course,  preferable  to  tank  steel,  but  the  best  practice 
demands  a  better  grade  for  high  quality  boiler  and  stand-pipe 
construction.  .  .  .  Flange  steel,  the  next  grade  above  shell 
steel,  is  distinguished  by  its  uniformity,  high  ductility,  and 
usually  low  tensile  strength.  It  is  the  grade  of  steel  plate 
adopted  in  the  best  practice  for  the  construction  of  steam- 
boilers  and  stand-pipes.  .  .  .  Ordinary  fire-box  and  locomo- 
tive fire-box  are  still  higher  grades  of  steel  boiler-plate,  pos- 
sessing special  properties  which  fit  them  for  the  uses  indicated 
by  their  trade  designations." 

The  matter  of  cost  naturally  has  a  distinct  influence  upon 
the  selection  of  grades  of  materials  to  be  used  in  stand-pipe 


7°  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

construction,  and  a  comparison  is  therefore  of  interest.  In 
July  of  the  present  year  (1900),  a  large  manufacturer  of 
boilers  and  stand-pipes  writes  as  follows : 

"  In  regard  to  the  price  of  steel  plates,  would  advise 

Tank  steel,  under  T3g  in.  at  mill $1.15 

"         "       above  \  in.  at  mill i.io 

Shell  steel 1.20 

Flange  steel 1.25 

Fire-box  steel 1.30  to  2.85 

Rivets i. 80 

In  addition  to  the  chemical  and  physical  specifications 
for  fixing  the  requirements  for  different  grades  of  steel,  it  is 
considered  good  practice  to  stipulate  certain  bending  and  drift 
tests,  depending  upon  the  nature  of  the  work  for  which  the 
steel  will  be  used.  The  Testing  Laboratory,  before  quoted, 
writes  in  this  connection,  "  These  tests  frequently  reject  mate- 
rial more  than  other  requirements,  as  they  more  clearly  show 
whether  the  material  will  stand  the  strain  for  which  it  is 
intended." 

The  specifications  for  plate  suggested  by  Prof.  Pence  for 
stand-pipe  material  is  as  follows:  "Material. — The  material 
composing  the  stand-pipe  shall  be  soft,  open-hearth  steel,  con- 
taining not  more  than  0.06$  phosphorus,  and  having  an  ulti- 
mate tensile  strength  of  not  less  than  54,000,  nor  more  than 
62,000,  Ibs.  per  sq.  inch;  an  elastic  limit  not  less  than  one- 
half  the  ultimate  strength,  an  elongation  of  not  less  than  26^ 
in  8  inches,  and  a  reduction  of  area  of  not  less  than  50$  at 
fracture,  which  shall  be  silky  in  character.  Before  or  after 
being  heated  to  a  cherry  red  and  quenched  with  water  at  80 
deg.  F.,  the  steel  shall  admit  of  bending  while  cold,  flat  upon 
itself,  without  sign  of  fracture  on  the  outside  of  the  bent 
portion." 

The  requirements  above  are  the  result  of  wide  investiga- 
tion by  Prof.  Pence,  and  plate  filling  these  specifications 


THE    USE   OF  IRON.  Jl 

would  certainly  prove  a  suitable  material,  whilst  the  stipula- 
tions are  not  so  severe  as  to  appear  too  arbitrary  or  such  that 
there  should  be  any  difficulty  upon  the  part  of  the  manufac- 
turer in  filling  the  order,  hence  the  market  quotation  upon 
such  plate  should  be  sufficiently  reasonable  as  to  permit  of  its 
use  for  such  structures. 

Practically  the  steel  called  for  by  Prof.  Pence  is  a  li  flange 
steel,"  worth,  according  to  the  quotations  above  cited,  $1.25 
per  100  Ibs.  f.  o.  b.  at  mill.  One  of  the  best  authorities  in  the 
United  States  writes  as  follows  regarding  structural  steel  for 
stand-pipe  work : 

"  In  the  matter  of  stand-pipe  construction,  the  quality  of 
the  steel  depends  a  good  deal  on  the  size  of  the  stand-pipe. 
That  is,  on  the  thickness  and  size  of  the  plates  which  you  are 
to  use.  Also  whether  you  are  going  to  drill  and  ream  the 
material.  Roughly  speaking,  the  specifications  should  be 
about  as  follows:" 

"  Soft  open-hearth  steel;  to  be  either  acid  or  basic;  tensile 
strength,  54,000  to  62,000  Ibs.  ;  elastic  limit  not  less  than 
33,000;  elongation,  26^;  reduction  of  area,  50$;  sulphur, 
if  acid  open-hearth  steel,  less  than  .06$;  phosphorus  less 
than  .075$.  If  basic  open-hearth  steel,  phosphorus  to  be 
under  .035  and  sulphur  under  .035$.  Bend  tests  should  be 
made  on  strips  about  I  j-  in.  wide,  planed  parallel,  and  then 
should  be  bent  180  degrees  flat  upon  themselves  without  show- 
ing sign  of  fracture  on  either  the  convex  or  concave  side  of  the 
curve.  This  test  should  be  carefully  carried  out  on  each  plate. 
Certain  drift  tests  should  also  be  made;  that  is,  a  hole  15-16  in. 
in  diameter,  or  whatever  size  the  rivet-hole  is,  should  be  drifted 
to  twice  its  size  without  cracking  or  injuring  the  plate." 

This  authority  practically  agrees  with  the  conclusions 
ascribed  to  Prof.  Pence  as  to  the  quality  of  steel  suitable  for 
stand-pipe  work.  As  has  been  shown,  the  thickness  of  plate 
affects  the  physical  properties,  and  should  therefore,  it  appears 


72  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

to  the  author,  be  considered  in  the  preparation  of  a  set  of 
specifications.  In  this  connection,  and  quoting  from  the 
"  Manufacture  and  Properties  of  Structural  Steel:"  "The 
effects  caused  by  variations  in  rolling  temperatures  appear  in 
their  most  marked  degree  in  the  comparison  of  plates  of  dif- 
ferent gauges.  It  is  not  customary  to  test  the  same  heat  in 
several  sizes,  but  by  long  experience  the  manufacturer  is  able 
to  judge  the  relative  properties  of  each  thickness.  The  heads 
of  two  widely  known  plate  mills  have  given  me  their  estimate 
that,  taking  one-half  inch  as  a  basis,  there  will  be  the  follow- 
ing changes  in  the  physical  properties  for  every  increase  of 
one  quarter  of  an  inch  in  thickness: 

(1)  A  decrease  in  ultimate  strength  of    1000  pounds  per 
square  inch. 

(2)  A  decrease  in  elongation  of  one  per  cent.,  when  meas- 
ured in  an  8  in.  parallel  section. 

(3)  A  decrease  in  reduction  of  area  of  two  per  cent. 

It  is  therefore  plain  that  in  writing  specifications  some 
allowance  must  be  made  for  these  conditions,  since  a  require- 
ment which  is  perfectly  proper  for  a  three-eighths  inch  plate 
will  be  unreasonable  for  a  plate  of  one  and  a  half  inches. 

"  Moreover  the  effect  is  cumulative,  since  a  hard  steel  must 
be  used  in  making  the  thick  plate,  and  this  will  tend  to  lessen 
the  difficulty  rather  than  make  up  for  the  reduction  caused  by 
the  larger  section.  In  plates  below  three-eighths  of  an  inch  in 
thickness  it  is  also  necessary  to  make  allowances,  since  it  is 
almost  impossible  to  finish  them  at  a  high  temperature,  and 
the  test  will  give  a  high  ultimate  strength  and  a  low  ductility." 

Whilst  it  may  appear  unnecessary  -to  exact  as  a  pre- 
requisite the  percentage  of  permissible  alloys,  other,  per- 
haps, than  phosphorus  and  sulphur,  it  may  not  be  amiss  to 
include  in  the  specifications,  certain  requirements  as  to  silicon 
and  manganese. 

In  the  "  Manufacture  and  Properties  of  Structural  Steel  '* 


THE    USE   OF  IRON.  ?$ 

appears  a  table  compiled  from  a  number  of  tests  of  groups  of 
specimens  from  both  acid  and  basic  manufacture,  and  from 
this  table,  two  groups  of  .109  %  carbon  steel  show  the  other 
elements  as  follows: 

(1)  Silicon  .008  ;  Manganese,    .310:  Sulphur,  .036 ;  Phosphorus,   .066 

(2)  "         .007;             "             .380;         "         .048;             "  .082 
Ultimate  strength  of  specimen    No.  I  (acid)    57,3io  Ibs. 

"  "         "          "          No.  2  (basic)     57,430   " 

According  to  table  showing  graduations  of  steels  in  relation 
to  their  percentages  of  carbon,  it  will  be  seen  that  this  steel 
will  grade  as  "soft";  ultimate  strength,  56,500;  elastic 
limit,  34,000  Ibs.  ;  stretch  in  8  in.,  30$;  reduction  of  fractured 
area,  56  #. 

It  is  impossible  at  this  time  to  reconcile  all  conclusions, 
and  theoretical  and  scientific  considerations  must  be  moulded 
more  or  less  to  fit  commercial  standards,  which  have  been 
largely  set  by  the  Association  of  American  Steel  Manufac- 
turers, whose  standard  specifications  are  the  result  of  much 
careful  consideration  and  study. 

Deviations  from  these  regulation  specifications  will  be 
found  to  entail  additional  expense  to  the  consumer,  possibly 
not  warranted  by  assumed  theoretical  conditions,  and  therefore, 
in  the  matter  of  physical  test  of  steel  required,  the  wording  of 
the  specifications  "  to  conform  to  the  standard  specifications 
of  the  Association  of  American  Steel  Manufacturers,"  would 
undoubtedly  cover  the  general  physical  requirements  for  a 
serviceable  steel  which  should  be  "  soft,"  52,000  to  62,000  Ibs. 
tensile  strength  per  square  inch. 

In  the  matter  of  the  chemical  specifications,  this  properly 
comes  within  the  province  of  the  engineer,  and  the  following 
is  suggested: 

CHEMICAL  SPECIFICATIONS. 

The  plate  metal  to  be  used  in  stand-pipe  construction 
shall  be  the  product  of  some  well-established  and  reputable 


74  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

mill  employing  the  "  open- hearth  process  of  manufacture,"  a 
preference  being  given  to  acid  furnace-lining  methods. 

The  chemical  qualifications  for  this  metal  shall  be  such  as 
to  ensure  the  reduction  of  the  metalloids  to  the  following 
limiting  maximum  percentages  in  the  finished  product : 

Phosphorus,  .08;  Sulphur,  .05;  Manganese,  .60;  Silicon,  .04. 

Drillings  for  chemical  analysis  may  be  taken  either  from 
test-piece  or  finished  product,  and  if  required,  each  of  the 
elements  may  be  ordered  determined. 

The  simple  tests  of  bending  and  drifting  should  be  inserted 
into  the  specifications  for  structural  metal.  It  should  be  pro- 
vided that  from  any  melt  or  number  of  melts,  test-specimens, 
as  strips,  might  be  cut  from  the  plate.  Such  strips  should  be 
about  \\  inches  in  width,  should  be  planed  parallel,  and, 
when  bent  180  degrees  upon  itself,  either  hot  or  cold, 
should  fracture  appear  upon  either  the  concave  or  convex  sur- 
faces of  the  curve,  the  melt  may  be  subject  to  rejection. 
Rejections  should  also  be  provided  for  if  the  material  will  not 
stand,  without  injury,  drifting  a  hole  in  test  pieces  to  twice  the 
original  diameter.  Such  holes  are  ordinarily  about  \\  in. 

Inspection. — That  there  may  be  no  uncertainty  or  disap- 
pointment as  to  results,  it  is  necessary  not  only  that  the 
constructive  engineer  shall  know  what  to  specify  in  ordering 
materials,  but  he  must  be  reasonably  sure  that  he  is  getting 
what  he  requires.  No  field-inspection  or  cursory  examination 
can  be  relied  upon  to  reveal  departures  from  the  specifications 
and  fatal  defects,  and  absolute  certainty  as  to  results  can  only 
be  secured  through  a  close,  systematic  inspection  during  the 
process  of  manufacture  from  the  raw  material  to  the  finished 
structure;  it  is  obvious,  therefore,  that  such  careful  attention 
to  details  requires  the  constant  presence  of  a  skilled  inspector 
at  the  mill,  the  shop,  and  in  the  field.  A  knowledge  of  and 
the  ability  to  conduct  the  necessary  series  of  chemical  and 


THE    USE   OF  IRON.  75 

physical  tests  is  rarely  possessed  by  the  designing  and  con- 
structing engineer,  even  though  it  were  possible  for  him  to 
give  his  personal  attention  to  these  details,  hence,  very  prop- 
erly, such  work  is  now  entrusted  to  an  assistant  making  a 
specialty  of  such  work,  or  most  usually  to  some  reputable 
inspection-bureau,  the  outgrowth  of  this  condition. 

The  necessity  for,  and  extent  of,  this  practice  is  clearly  ex- 
plained in  a  recent  paper  entitled  "Shop  and  Mill  Inspec- 
tion," by  Mr.  W.  O.  Henderer,  read  before  the  Civil  Engi- 
neers' Club  of  Cleveland,  and  from  which  the  following  is 
quoted  : 

"There  was  a  time  when  one  man  could  comfortably 
attend  to  such  duties  himself,  and  personally  follow  the  prog- 
ress of  the  material  in  all  its  various  processes.  The  shops 
and  mills  at  which  iron  was  manufactured,  and  where  the  fin- 
ished parts  of  structures  were  produced,  were  often  one  and 
the  same ;  or,  if  not,  the  processes  followed  each  other  in  such 
rotation  that  one  man  could  get  from  mill  to  shop  and  keep 
proper  consecutive  track  of  the  work.  But  the  industry  has 
of  late  years  grown  to  such  enormous  proportions  and  has  ex- 
tended over  such  a  large  area  that  it  is  impossible  for  one 
man  to  properly  inspect  the  work  in  all  its  stages.  Bridge 
companies  now  have  a  number  of  mills  from  which  to  order 
the  material  necessary  for  their  work.  They  are  likely  to 
have  plates  from  one  mill,  beams  and  channels  from  another, 
and  other  shapes  from  still  a  third ;  and  the  mills  are  often 
great  distances  apart.  Frequently,  too,  the  shop  is  at  work 
on  some  portions  of  a  contract  while  the  mills  are  still  fur- 
nishing materials.  It  is  manifestly  out  of  the  question  for 
any  one  man  to  thoroughly  inspect  work  at  all  these  places  at 
one  time.  He  must  have  assistance  in  some  way. 

"  Men  who  have  become  expert  and  experienced  in  this 
sort  of  work  have  made  inspection  their  particular  business, 
performing  this  service  at  a  compensation  based  on  the  ton- 


76  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

nage  in  the  work,  instead  of  entering  the  service  of  the  engi- 
neer or  architect  in  charge  at  a  salary.  Such  men,  as  they 
found  it  impossible  to  economically  perform  their  duties  per- 
sonally on  account  of  the  excessive  expenses  of  travelling 
about,  adopted  the  method  of  reciprocating  among  them- 
selves, an  inspector  in  Pittsburg  undertaking  to  do  the  mill- 
inspection  on  one  piece  of  work  for  another  located  in  Phila- 
delphia, while  the  latter  attended  to  shop-inspection  at  shops 
in  his  vicinity  for  the  former.  Naturally,  from  such  alliances 
among  inspectors,  there  has  resulted  the  formation  of  inspec- 
tion-bureaus or  companies.  Such  companies  employ  men 
permanently  at  the  various  mills  and  shops,  and  maintain 
extensive  general  offices,  at  which  the  clerical  work  of  copy- 
ing and  forwarding  reports  and  tests,  progress  of  work,  etc., 
is  performed.  By  securing  large  quantities  of  inspection 
work  they  are  able  to  keep  good  men  at  all  the  localities 
necessary,  maintaining  a  perfect  system  of  effective  inspection 
and  giving  their  clients  regular  reports  of  the  quality  of 
material  and  workmanship,  the  progress  of  the  work,  and 
information  as  to  tests,  shipments,  etc.,  which,  when  com- 
pleted, comprises  an  accurate  record  of  the  structure  in 
question,  and  surety  that  it  is  built  as  it  should  be.  .  .  .  The 
employment  of  competent  inspection-bureaus  becomes  more 
and  more  general  as  the  iron  and  steel  industry  increases  in 
volume,  and  competition  amongst  the  manufacturers  grows 
keener.  Men  are  realizing  more  and  more  forcibly  the  neces- 
sity for  such  services  in  order  to  secure  good  results.  The  day 
when  people  thought  that  because  a  bridge  was  built  of  iron 
it  would  stand  indefinitely  is  past  and  gone.  Men  are  finding 
that  there  is  good  and  bad  iron  and  steel,  and  that  there  is  a 
great  difference  between  them— often  the  difference  between 
success  and  failure,  between  a  strong,  stiff,  and  durable  struc- 
ture and  an  accident  costing  human  life — that  it  pays  to  spend 
the  small  added  cost  to  insure  the  use  of  good  material  and 
to  detect  and  exclude  the  bad. 


THE    USE    OF  IRON. 


77 


11  It  is  remarkable  that  so  many  fail  to  see  that  specifica- 
tions and  inspection  must  always  go  hand  in  hand ;  that 
neither  can  confer  the  benefits  it  should  without  the  other. 
Most  people  realize  that  if  no  specifications  are  stated  to  indi- 
cate the  nature  and  quality  of  the  structure  desired,  the  manu- 
facturer cannot  be  blamed  if  the  structure  does  not  meet  the 
expectations  of  the  purchaser.  But  often  little  thought  is 
given  to  the  second  part  of  the  purchaser's  duty,  that  of 
inspection.  It  is  not  recognized  as  a  duty  owed  by  every 
purchaser  for  his  own  protection  and  safety,  and  to  secure 
benefits  from  a  carefully  compiled  specification.  When  the 
millennium  is  reached,  when  it  may  be  reasonably  expected 
that  every  man's  work  will  be  perfect  and  each  one's  labor  as 
valuable  as  that  of  his  fellows,  then  there  will  be  no  differ- 
ence between  good  and  bad,  no  possibility  of  errors  or  mis- 
takes or  dishonesty.  When  that  time  arrives  there  will  be  no 
further  use  for  either  specifications  or  inspection,  and  many  a 
busy  man  will  loose  his  job.  But  until  that  time  there  will 
be  varying  grades  in  the  quality  of  materials  and  workman- 
ship, and  the  necessity  for  specifying  the  grade  desired  on 
any  piece  of  work  will  remain. 

"And  just  so  long  as  there  is  any  cause  or  reason  for 
specifications,  just  so  long  will  the  inspector  be  needed  to  see 
that  the  specifications  are  carried  out." 

Concerning  the  character  of  the  inspection  and  cost  for 
same,  Mr.  Henderer  continues:  "  There  are  a  few  inspection- 
bureaus  who  are  striving  for  the  improvement  of  inspection 
services,  through  the  establishment  of  carefully  devised  sys- 
tems for  the  thorough  handling  of  the  work  and  the  employ- 
ment of  only  experienced  and  thoroughly  reliable  men.  Such 
companies  can  and  do  give  the  quality  of  service  that  makes 
inspection  thoroughly  valuable.  But  they  have  thus  far 
found  themselves  seriously  handicapped  by  the  many  irre- 
sponsible inspectors  who  undertake  work  at  ridiculously  low 


78  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

prices  without  any  idea  of  doing  it  as  it  should  be  done. 
Engineers  and  architects  are  not  a  little  to  blame  for  this 
state  of  things,  since  too  many  of  them  fail  to  consider  the 
inspection  service  as  one  having  degrees  of  quality.  They 
have  become  accustomed  to  consider  that  all  inspection  is  the 
same,  and  to  require  that  each  inspector  who  makes  applica- 
tion for  their  work  shall  submit  his  prices  in  competition  with 
any  one  else  who  may  be  an  applicant,  and  then  employ  the 
man  with  the  lowest  price  without  taking  the  trouble  to 
properly  investigate  the  comparative  facilities  or  reputations 
of  the  applicants. 

"  It  cannot  be  expected  that  the  best  results  of  inspection 
will  be  gained  by  crowding  the  price  for  such  services  down 
to  the  lowest  possible  figure.  There  is  a  limit  below  which 
good  inspection  cannot  be  performed.  The  only  way  in 
which  an  engineer  can  get  the  full  benefit  that  inspection  can 
confer  is  to  determine  at  the  outset  to  pay  a  fair  price  for 
that  service,  and  then,  before  appointing  an  inspecting  firm, 
to  look  carefully  into  the  reputations  of  the  different  inspect- 
ing companies  available,  by  references  to  other  engineers  and 
to  pieces  of  work  that  have  been  inspected  by  them. 

"  Thorough  and  complete  inspection  of  iron  and  steel 
structural  material  should  generally  be  worth  one  dollar  per  net 
ton  of  shop  shipping-weights.  At  times,  and  under  especially 
favorable  conditions  as  regards  the  location  of  the  bureau's  em- 
ployes, it  can  be  done  for  less.  On  some  small  jobs  it  may 
be  more,  but  there  is  in  general  a  chance  for  the  inspector  to 
make  a  fair  living  at  that  average  price.  Such  inspection 
should  include  the  careful  comparison  and  checking  of  work- 
ing plans,  and  complete  supervision  and  tests  by  thoroughly 
experienced,  expert,  and  reliable  men  throughout  the  manu- 
facture of  the  material  from  the  time  it  is  first  produced  until 
it  is  shipped  from  the  shop." 


CHAPTER    IV. 
STRESS  OR  STRAIN. 

"STRESS"  or  "strain"  is  the  name  designating  the  ap- 
plication of  forces  to  a  body  in  the  same  straight  line  but  in 
opposite  directions,  so  that  the  internal  resistance  offered  by 
the  cohesive  force  of  the  fibres  or  particles  of  which  the  body 
is  composed  is  balanced  by  the  opposing  or  exterior  force  or 
pressure. 

The  effect  of  an  exterior  force  acting  upon  a  body  to 
change  its  shape,  may  be  exerted  as  "tension,"  "compres- 
sion," or  "  shear." 

If  the  force  acting  upon  a  body  has  a  tendency  to  elon- 
gate or  stretch  its  fibres  to  the  point  of  rupture  by  pulling 
them  apart,  this  force  is  termed  a  "  tensile  stress." 

If,  on  the  contrary,  the  application  of  the  force  tends  to 
shorten  or  to  compress  these  fibres,  such  force  is  called  a 
"compression  stress,"  obviously  "compression  "  and  "ten- 
sile" stresses  differ  only  as  regards  the  direction  in  which 
the  exterior  force  is  applied  or  exerted  upon  the  fibres  of 
which  the  body  consists. 

Force  applied  so  as  to  act  longitudinally  along  any 
"  member"  of  a  structure  through  its  fibres,  tends  either  to 
elongate  or  to  compress  these  fibres  in  direct  proportion  to- 
the  pressure  exerted,  and  the  resistance  offered  to  this  pressure 
by  the  fibres  themselves  is  also  directly  proportional  to  the 
tenacity  and  number  of  the  fibres  of  which  the  body  is  com- 
posed, as  represented  by  its  area  or  "cross-section." 

Beside  these  two  stresses,  there  is  a  third,  called  a  "shear 
stress,"  and  which,  as  its  name  would  indicate,  is  the  tendency 

79 


SO  TOWERS  AND  TANKS  FOR    WATER-WORKS. 

of  the  external  force  to  cut  in  twain  or  to  shear  the  fibres, 
and  is  the  application  of  the  forces  in  vertical  planes  at  right 
angles  to  the  fibres,  or  through  the  cross-section  of  the  body. 

The  consideration  and  understanding  of  these  stresses  in 
the  material  and  members  of  such  structures  as  towers,  tanks, 
and  the  like,  and  a  knowledge  of  the  resistance  which  the 
character  of  the  material,  its  dimensions,  and  shape,  will  offer 
in  opposition  to  extraneous  forces  is  of  the  utmost  im- 
portance. 

The  manner  or  method  of  the  application  of  force  to  a 
body  necessarily  comprehends  a  principle  of  mechanics  known 
as  the  "  moment"  of  forces,  or  the  tendency  of  a  force  to 
produce  motion  about  a  point.  This  is  an  expression  repre- 
senting the  power  produced  by  the  force  to  cause  motion 
about  a  point  when  acting  through  the  principle  of  "lever- 
age." 

In  the  consideration  of  the  stability  of  a  structure  or  its 
ability  to  resist  a  sliding,  horizontal  motion,  or  a  tendency  to 
overturn  about  its  toe,  the  consideration  and  application  of 
the  principles  of  "leverage,"  and  the  opposing  force  exerted 
by  the  natural  law  of  gravitation,  must  be  carefully  analyzed 
and  observed. 

Moment  of  Forces. — The  '  *  moment  "  of  a  force  is  the  prod- 
uct of  the  force  by  its  leverage ;  thus,  if  the  force  or  pres- 
sure be  represented  by  pounds,  tons,  etc.,  and  the  leverage 
of  the  force,  or  the  perpendicular  or  shortest  distance  from 
its  "fulcrum"  to  the  direction  through  which  the  force  is 
acting  is  expressed  in  feet,  this  product  is  termed  the 
"moment"  of  the  force  about  the  given  point,  and  may  be 
expressed  as  "  foot-pounds  or  "  foot-tons." 

If  any  force,  as  10  pounds,  10  tons,  etc.,  be  exerted 
through  a  leverage  of  any  number  of  feet,  say  20,  the  result- 
ant, 10  X  20  equals  200  feet-pounds  or  feet-tons. 

The  resistance  which  the  weight  of  a  structure,  acting  ver- 


STRESS    OR    STRAIN.  8 1 

tically  through  its  centre  of  gravity,  offers  to  an  applied  force 
through  its  leverage  and  tending  to  change  its  position  de- 
termines its  "  stability  of  position." 

Equilibrium. — Forces  are  said  to  be  in  "  equilibrium " 
when  they  equal  or  balance  each  other,  each  preventing  the 
other  from  imparting  motion  to  the  body;  so  also  forces, 
when  multiplied  by  their  respective  leverages,  are  said  to  be  in 
equilibrium  when  the  action  which  each  exerts  maintains  the 
body  at  rest,  and  it  may  be  observed  that  the  moment  of  forces 
about  a  point  may  hold  each  other  and  establish  the  equilib- 
rium of  the  body  even  though  the  forces  themselves  fail  to 
balance.  Two  opposing  forces,  or  the  moment  of  these 
forces,  acting  at  the  same  time  equally  upon  an  unresisting 
body,  neutralize  or  destroy  each  other,  the  body  is  at  rest  and 
equilibrium  is  said  to  exist.  Should  one  force,  or  the  moment 
of  that  force,  exceed  the  other,  equal  parts  of  each  force  des- 
troy each  other  and  any  excess  of  the  one  over  the  other  is 
termed  the  ''resultant"  of  the  two  forces;  and  the  direction 
of  this  excess,  or  the  resultant  of  the  two  forces,  is  exerted  in 
a  line  bisecting  the  original  angle  at  which  the  forces  met,  'and 
the  extent  of  the  force  exerted  by  this  resultant  is  the  dif- 
ference between  that  offered  by  the  two  or  more  original 
forces,  or  the  moment  of  those  forces. 

Resistance  to  Overturning. — In  analyzing  the  stability  of 
any  structure  such  as  a  stand-pipe,  the  effect  of  the  pressure 
exerted  by  the  wind  against  the  sides  of  the  tank  is  to  cause 
motion  by  a  sliding,  horizontal  movement,  and  to  produce 
overturning  about  the  toe  or  base.  This  tendency  is  resisted 
by  the  weight  of  the  tank  itself,  acting  vertically  through  its 
centre  of  gravity  and  upon  the  area  of  its  base.  The  dispo- 
sition toward  moving  horizontally  upon  its  base  is  opposed  by 
the  roughness  of  the  parallel  faces  in  contract,  as  the  bottom 
plates  of  the  tank  and  the  upper  face  of  the  foundations,  and 
is  found  by  multiplying  the  perpendicular  pressure  by  the 
4t  coefficient  of  friction,"  but  as  against  the  action  of  the 


82 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 


wind  upon  the  sides  of  a  stand-pipe,  the  vertical  pressure  ex- 
erted even  by  the  weight  of  the  empty  tank  over  the  area  of 
its  base,  is  usually  sufficient  to  restrain  the  force  exerted  by 
the  wind  and  to  keep  the  structure  at  rest  even  without  the 
customary  anchorage,  therefore  this  tendency  will  not  be 
given  further  consideration  here. 

The  effect  which  wind  exerts  upon  cylindrical  structures 
such  as  a  stand-pipe  has  never  been  determined  with  any  de- 
gree of  certainty,  but  Trautwine  has  the  following: 

Wind  Pressure. — "The  relation  between  the  velocity  of 
wind  and  its  pressure  against  an  obstacle  placed  either  at 
right  angles  to  its  course,  or  inclined  to  it,  has  not  been  well 
determined,  and  still  less  so  its  pressure  against  curved  sur- 
faces. The  pressure  against  a  large  surface  is  probably  pro- 
portionately greater  than  against  a  small  one.  It  is  generally 
observed  to  vary  nearly  as  the  square  of  the  velocities,  and 
when  the  obstacle  is  at  right  angles  to  its  direction,  the  pres- 
sure in  pounds  per  square  foot  of  exposed  surface  is  considered 
to  be  equal  to  the  square  of  the  velocity  in  miles  per  hour, 
divided  by  200.  On  this  basis,  which  is  probably  quite  defec- 
tive, the  following  table,  as  given  by  Smeaton,  is  prepared  :  " 


Velocity  in  Miles 
Per  Hour. 

Velocity  in  Feet 
Per  Second. 

Pressure  in  Pounds 
Per  Square  Foot. 

Remarks. 

I 

1.467 

.005 

Hardly  perceptible. 

2 

2-933 

.O2O 

Pleasant. 

3 

4.400 

•045 

4 

5.876 

.080 

5 

7-33 

.125 

10 

1467 

•  5 

12* 

18-33 

.781 

Fresh  breeze. 

15 

22. 

1.125 

20 

29-33 

.     2. 

20 

36.67 

3-125 

Brisk  wind. 

30 

44. 

4-5 

Strong  wind. 

40 

58.67 

8. 

High  wind. 

50 

7333 

12.5 

Storm. 

60 

88. 

18. 

Violent  storm. 

80 

117.3 

32. 

Hurricane. 

IOO 

146.7 

50. 

Violent  hurricane. 

OR   STRAIN. 


The  formula  employed  by  Smeaton  in  the  preparation  of 
the  foregoing  table,  and  where  P  =  pressure  in  pounds  per  square 
foot  of  surface  and  V  =  velocity  of  the  wind  in  miles  per  hour, 
was  P  =  0.0050 F2. 

The  U.  S.  Water  Bureau  uses  the  same  formula  except  that 
the  coefficient  is  made  0.0040. 

The  coefficient  used  was  determined  experimentally  by  ex- 
posing squarely  against  the  wind  plates  of  from  four  to  nine 
square  feet  of  surface  and  recording  simultaneously  the  velocity 
of  the  wind  and  its  resulting  pressure. 

The  anemometer,  the  instrument  used  for  measuring  wind 
velocities,  gives  readings  which  only  approximate  the  real  veloc- 
ities, the  latter  being  found  by  correction.  The  following  table, 
taken  from  a  circular  issued  by  the  U.  S.  Department  of  Agri- 
culture, Weather  Bureau,  gives  the  recorded  or  indicated  veloc- 
ities, their  equivalent  corrected  velocities,  and  the  corresponding 
pressures. 

TABLE  OF  WIND  PRESSURES. 


Indicated  Vel. 

True  Vel. 

Pounds  Pressure. 

id  miles. 

9.6  m 

les. 

0.369  per  sq.ft. 

20        * 

17.8 

1.27 

3° 

25-7 

2.64 

40 

33-3 

4-44 

S° 

40.8 

6.66 

60 

48.0 

9.22 

70 

55-2 

12.20 

80 

62.2 

IS-50 

90 

69.2 

19.20 

Prof.  C.  F.  Marvin,  of  the  Weather  Bureau,  states  that  ve- 
locities beyond  50  to  60  miles  an  hour  are  not  accurately  recorded 
by  the  anemometer,  and  that  exact  information  is  therefore 
impossible,  although  cases  are  reported  where  the  anemometer 
has  continuously  indicated  velocities  as  great  as  80  to  100 
miles  per  hour,  but  exact  data  for  interpreting  such  indications 


84  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

does  not  exist;  therefore  the  exact  wind  movement  cannot  be 
reduced.  Occasionally, '  during  the  thunder-storms  and  gusts 
of  summer,  anemometers  will  record  for  a  brief  period  velocities 
up  to  75  miles  an  hour;  but  in  such  cases  the  storms  and  gusts 
are  of  short  duration.  It  is,  however,  reported  that  at  some 
seacoast  stations  and  at  Mount  Washington,  N.  H.,  velocities 
as  great  as  100  miles  per  hour  have  been  continuously  recorded 
during  pronounced  storms.  Occasionally  during  storms,  sudden 
and  violent  gusts  of  wind  occur,  considerably  greater  than  the 
indicated  or  mean  velocities.  The  impact  of  such  gusts  upon 
engineering  structures  are  likely  to  set  up  coincident  vibration 
out  of  proportion  to  the  effect  of  the  recorded  velocities  of  the 
wind.  In  an  article  in  the  Engineering  News,  Dec.  13,  1890, 
Prof.  Marvin  states  that  momentary  pressures  as  great  as  35% 
in  excess  of  the  recorded  mean  pressures  may  continually  occur 
and  recur,  and  if  their  rate  of  occurrence  be  at  all  synchronous 
with  the  natural  time  of  vibration  of  the  structure  or  any  part 
thereof,  remarkable  results  may  follow.  The  greatest  velocity 
so  far  registered  is  reported  from  the  signal  station  at  Point 
Reyes,  CaL,  where  on  May  18,  1902,  a  wind  velocity  of  102 
miles  an  hour  was  registered,  and  for  several  moments  the 
anemometer  recorded  a  velocity  of  120  miles  an  hour,  the 
violence  of  the  storm  finally  ripping  the  cups  from  the  instru- 
ment. During  72  hours,  the  record  was  4701  miles. 

The  assumption  given  above,  that  the  pressure  of  the  wind 
acting  upon  a  semi- cylindrical  surface  is  equal  to  one  half  that  which 
would  be  exerted  upon  a  flat  surface,  having  an  area  equal  to 
that  of  the  diametral  plane  of  the  cylinder,  is  generally 
accepted  as  nearly  correct  by  the  best  authorities,  and 
accords  with  the  recommendation  of  Rankine  in  Applied 
Mechanics. 

In  assuming  the  maximum  pressure  of  the  wind,  it  is 
considered  good  practice  to  accord  it  a  pressure  of  about  30 


S2'X£SS  OK  STRAIN. 


Ibs.  per  square  foot  and  estimated  as  being  exerted  upon 
the  vertical  plane  as  projected  through  the  centre  of  gravity 
of  a  cylindrical  structure;  thus,  to  estimate  the  maximum 
pressure  of  the  wind  exerted  upon  the  semi-cylindrical  sides 
of  a  stand-pipe  20  ft.  in  diameter  and  120  ft.  in  height, 
20  X  I2°  X  30  Ibs.  equals  72,000  Ibs.  or  36  tons,  and  the 
moment  of  this  force,  or  the  pressure  in  tons  multiplied  by 
its  leverage,  or  its  distance  from  the  centre  of  gravity  about 
the  point,  is  60  ft.  X  36  tons,  or  2,160  ft. -tons. 

The  resistance  offered  to  this  overturning  moment  is  the 
weight  of  the  structure,  in  tons,  multiplied  by  its  leverage, 
or  its  perpendicular  distance  from  its  centre  of  gravity  at  its 
base  to  the  point  or  toe,  and  as  the  centre  of  gravity  of  a 
cylinder  is  the  centre  of  the  circle,  the  leverage  is  therefore 


FlG.  8. — The  pressure  against  a  semi-cylindrical  surface  abcnom  is  about 
one  half  that  against  the  flat  surface  abnm. 

its  radius,  or  in  this  case  10  ft.,  so  that  the  moment  of  this 
force  is  its  weight,  say  80  tons,  multiplied  by  its  lever-arm, 
10  ft.,  or  800  ft. -tons,  therefore  the  resultant  of  these  two 
moments  shows  an  excess  of  1360  ft. -tons,  in  amount  and 
tendency  sufficient  to  render  the  structure  unstable  or  to 
cause  its  overturning.  In  order,  therefore,  to  render  such  a 
structure  stable  upon  its  foundations,  it  will  be  necessary  to 
provide  a  suitable  anchorage.  In  order!  to  show  the  instabil- 


86 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 


W 

1  120  Feet.  * 

CO 

\ 

1 

\ 

: 

8 

\   \ 
I    \ 

I 

II 

\     \ 

1 

\      \ 

\      \ 

™ 

•       \ 

'    \        v 

R 

\ 

\ 

\ 

I 

\ 

I 

131  Tons 

I 
I 
\ 
I 

\ 

\ 

\ 

| 

I 

\ 

Anchorage 

I 
i 
\ 
\ 
\ 
\ 

R 
I 

\ 
\ 
\ 
\ 

\ 

\ 
\ 
\ 

i 

\ 

I 

\ 

\ 

\ 

y                 \ 

\ 

\ 

\ 

—  Base  20  Feet   —*1 

™ 

FIG.  9. 


OR   STRAIN.  87 

ity  of  such  a  structure  graphically,  lay  off,  by  scale,  a  figure 
20  X  120,  denoting  its  centre  of  gravity  G.  Draw  the  hori- 
zontal line  GW  to  any  convenient  scale,  representing  the 
estimated  force  of  the  wind  in  tons.  By  the  same  scale,  draw 
a  vertical  line,  GV,  showing  the  direction  and  amount  of  the 
vertical  forces  due  to  the  weight  of  the  structure.  Complete 
the  parallelogram  of  forces  as  shown,  and  the  diagonal,  GRy 
will  represent  the  direction  and  extent  of  the  combined  action 
of  the  vertical  and  horizontal  forces,  and,  if  produced,  falls 
without  the  figure  or  beyond  its  base.  Here  the  structure 
can  not  stand. 


Wind 


FIG  90. 

In  order  to  secure  the  equilibrium  of  the  structure  it  is 
evident  that  some  form  of  anchorage  must  be  provided.  Con- 
sidering the  wind-stress  to  which  the  tank  may  be  subjected,  the 
moment  of  this  force  M,  is  72,000  Ibs.  multiplied  by  the  leverage 
in  inches,  720,  or  51,840,000  pounds-inches. 

The  area  of  the  tank  cross-section  in  inches  being  45,239, 


87 a  TOWERS  AND   TANKS  FOR  WATER  WORKS. 

the  maximum  bending  moment  per  square  inch  of  circumfer- 
ence S,  =  -r\  or  1146,  which  value  muitiplied  by  the  length  of 

A 


FIG.  9&. — Anchorage  for  24  ft.  X  70  ft.  Stand-pipe. 

the  arc  between  anchors  (753.96  inches  divided  by  the  number 
of  rods,  say  8)  gives  94.24  inches,  which  multiplied  by  the  bend- 
ing moment  1146  gives  107,599  Ibs.  as  the  total  wind  reaction 


STRESS  OR  STRAIN. 


876 


on  any  one  rod.  Against  this  wind  pressure  the  force  of  the 
load  due  to  the  tank  weight  or  metal  is  opposed  and  must  be 
considered. 

If  W  =  the  total  "dead"  load  (160,000 Ibs.)  and  the  number 
of   rods,    N  =  8,    then    the    net    maximum    reaction    will    be 

W 

•^r±wind  reaction  or  87,599  ^s.  in  the  case  under  consideration. 

The  maximum  reaction  will  occur  at  E,  Fig.  90,  when  the 
wind  is  as  shown. 


FIG.  gc. — Connection  Details. 

Assuming  15,000  Ibs.  as  a  safe   working  value  or  allowable 
stress  for  the  rod  metal,  we  have  -^-^-  =  5. 833  square  inches  of 

rod  cross- section  and  the  nearest  approximate  size  is  2f  inches. 
The  anchors  at  A  and  B,  Fig.  90,  being  on  the  neutral  axis 
when  the  wind  is  as  shown,  receive  no  longitudinal  strain  as  no 
fiber  stresses  occur  at  the  neutral  axis  within  the  elastic  limit, 

and  the  pull  on  the  rods  Cf  and  D  is  S  =  J  -j TT. 


88  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

Assuming  that  the  three  rods,  C,  D  and  E,  are  in  tension 
and  are  capable  of  exerting  a  holding  down  value  of  87,599  Ibs. 
each,  the  three  would  exert  an  effect  equal  to  approximately  131 
tons,  which  would  be  added  to  the  dead  weight  and  measured 
along  the  vertical  line  G-V,  Fij.  9,  proving  graphically  the 
stability  of  structure. 

The  maximum  stress  per  circumferential  inch  is  the  bending 
moment  divided  by  the  area,  or,  S  +  M  +  A;  this  value  when 
multiplied  by  the  length  of  the  arc  between  anchor  rods  gives 
the  maximum  wind-stress  on  each  rod.  The  net  stress  is  found 
by  dividing  the  weight  of  metal  by  the  number  of  rods  and 
subtracting  from  the  maximum  stress,  thus  S  =  M  +  A  —  W  +  N. 

Hydrostatic  Pressure. — In  addition  to  the  external  pres- 
sure exerted  by  the  wind,  stand-pipes  are  subject  to,  and  must 
be  designed  to  resist,  an  internal  pressure  of  water  with  which 
they  will  be  rilled,  or  to  resist  the  "  Hydrostatic  Pressure." 
From  experiment  it  has  been  found  that  the  maximum  densi- 
ty of  water  occurs  at  from  6  degrees  to  7  degrees. above  freez- 
ing point,  from  which  point  its  density  decreases  and  volume 
increases  with  each  degree  of  advancing  temperature. 

At  the  level  of  the  sea,  the  approximate  atmospheric  pres- 
sure of  14%  Ibs.  per  sq.  in.  will  balance  a  column  of  water  34 
ft.  in  height.  The  weight  of  water  is  approximately  62  J  Ibs. 
per  cubic  foot,  and  is  usually  so  taken  for  the  purpose  of  cal- 
culation. A  cubic  foot  of  water,  in  a  cubical  receptacle,  exerts  a 
pressure  over  the  base  of  I44sq.  inches,  equivalent  to  its  weight ; 
so  then,  the  pressure  of  62^  Ibs.  of  water  over  144  sq.  inches 
(6_|:5.)  equals  0.433507  Ibs.  ;  hence,  to  find  the  pressure  of  any 
column  of  water,  multiply  the  height  or  "head  "  in  feet  by 
.434;  very  roughly,  divide  the  given  head  by  2. 

Conversely,  when  the  pressure  per  sq.  inch  is  given,  to 
find  the  head  to  which  the  pressure  is  due,  -££%  equals  2.30677, 
or  roughly,  2.3.  The  following  table  may  be  found  useful: 


STfi£SS  Off  STRAIN. 


89 


Converting  Feet-head  of  Water  into 
Pressure  per  Square  Inch. 

Converting  Pressure  per  Square  Inch  into 
Feet-head  of  Water. 

Feet-head. 

Pounds  per 
Square  Inch. 

Pounds  per 
Square  Inch. 

Feet-head. 

jO       ....           

4-33 
6.  50 
8.66 
10.83 
12.99 
15.16 
I7-32 
19.40 
21.65 
23.82 

25-99 
28.15 
30  32 
32.48 
34-65 
36-81 
38-98 
41.14 
43-31 
45-57 
47.64 
49.91 
51.97 
54-25 
56.30 

58-59 
60.63 
62.93 
64.96 

e 

11-54 

I3-85 
16.16 
18.47 
20.78 
23.09 
34-63 
46.18 
57-72 
69.27 
80.  81 
92-36 
103.90 

H5-45 
126.99 

138.54 
150.08 
161.63 

I73-I7 
184.72 
196.26 
207.81 

219-35 
230  .  90 
253-98 
277.07 
300.16 
323-25 
346.34 

6  

20 

oe 

g 

•JQ  

•3  C       . 

10 

»1O 

T  C 

AS,  .  . 

2O  

en 

oe. 

c  e  .  . 

OQ 

60            

".e     . 

6=.  . 

AQ                  

4.5  .  . 

•re 

eo 

So 

e  e 

«c 

6O    -  . 

QO 

6^.. 

QC 

7O.  . 

100        

7C  .  . 

IQC  .  , 

80  

no  

8e.  . 

lie  .  . 

QO 

100  

T7O 

I  IO 

T  7C 

1  2O 

uo 

I^O 

14.  c, 

I4O  .  . 

ICQ 

In  considering  the  effect  of  the  pressure  due  to  the  height 
or  head  of  water,  or  "  static  head,"  exerted  upon  the  inter- 
ior surfaces  of  a  cylindrical  structure  such  as  a  stand-pipe,  the 
explanation  given  by  Trautwine  is  so  concise  and  clear  that  it 
is  copied  here  without  further  apology : 

"  In  the  figure,  which  represents  a  vessel  full  of  water,  the 
total  pressure  against  the  semi-cylindrical  surface  a  v  e  m  d  k 
and  perpendicular  to  it,  must  be  also  horizontal,  because  the 
surface  is  vertical ;  but  inasmuch  as  the  surface  is  curved,  this 


90  TOWERS  AND    TANKS  FOR    WATER- WORKS. 

total  pressure  acts  against  it  in  many  directions,  which  might 
be  represented  by  an  infinite  number  of  radii  drawn  from  o  as 
a  centre.  But  let  it  be  required  to  find  the  horizontal  pres- 
sure in  Ibs.  in  one  direction  only,  say  parallel  to  o  e,  or  perpen- 
dicular to  a  d,  which  would  be  the  force  tending  to  tear  the 
curved  surface  away  from  the  flat  sides  a  b  n  v,  and  d  c  s  k, 
by  producing  fractures  along  the  lines  a  v  and  d  k,  or  which 
would  tend  to  burst  a  pipe  or  other  cylinder.  In  this  case> 
multiply  together  the  area  of  the  vertical  projection  a  dkv  in 
sq.  feet;  the  depth  of  the  centre  of  gravity  of  the  curved  sur- 
face in  ft.  (which  in  the  semi-cylinder  would  be  half  of  e  m> 
or  of  o  z),  and  62.5. 

'*  Since  the  resulting  pressure  is  resisted  by  the  strength  of 
the  vessel  along  the  two  lines  a  v  and  d  k,  it  is  plain  that 
each  single  thickness  along  those  lines  need  only  be  sufficient 
to  resist  safely  one-half  of  it ;  and  so  in  the  case  of  pipes  or 
other  cylinders,  such  as  hooped  cisterns  or  tanks." 

a       b 


FIG.  10. 

Resistance  offered  by  Material. — From  the  above,  it  will 
be  seen  that  a  formula  for  hydrostatic  pressure  exerted 
upon  the  sides  of  a  cylinder  would  be 

D  X  HX  62.5 

-jr    ->  (?) 

where  D  =  diameter  of  cylinder ; 
H  =  its  height  in  feet. 


• 

STABILITY  OF  Sl^RUCTURE.  91 

It  has  been  shown  that  the  pressure  exerted  upon  the  bot- 
tom of  the  vessel  is  in  direct  proportion  to  the  head  of  water, 
or  the  area,  multiplied  by  the  head  of  the  column  in  pounds. 

To  resist  the  internal  hydrostatic  stresses  is  opposed  the 
thickness  and  material  of  the  plate  and  its  riveting  in  a  cyl- 
indrical stand-pipe,  and  to  proportion  the  opposing  plate 
to  safely  resist  the  pressure  the  following  factors  must  be 
known  or  assumed:  1st,  The  tensile  strength  of  the  metal; 
2d,  the  percentage  of  strength  of  the  material;  3d,  a  reduc- 
tion of  theoretical  strength  to  allow  a  margin  or  factor  of  safe- 
ty ;  and  4th,  some  unit  of  length  must  be  adopted  repre- 
senting the  surface  pressed.  The  unit  of  length  is  usually 
taken  for  convenience  at  12  in.  In  designing,  60,000  Ibs.  per 
sq.  in.  is  generally  assumed  as  the  unit  stress  of  the  material, 
and  allowance  for  the  decreased  value  of  this  unit,  due  to 
punching  and  riveting,  is  made  at  about  33  per  cent,  off,  or  the 
working  value  of  a  12  in.  section  is  at  f  of  its  original  strength  ; 
reducing  the  ultimate  strength  by  using  a  factor  of  safety  of 
4  is  considered  good  practice  for  such  metal  structures,  not 
subject  to  shock,  hence  the  formula  for  proportioning  the 
thickness  of  plates  intended  to  resist  such  hydrostatic  pres- 
sures may  be  given  as 

60,000  X  12"  X  |  .. 

4 

To  proportion  the  thickness  of  metal  intended  to  resist  the 
hydrostatic  pressure  exerted  upon  the  internal  surface  of  any 
cylinder,  divide  (i)  by  (2),  therefore  the  following  general  ex- 
pression for  the  thickness  of  metal  in  decimals  of  an  inch  for 
any  given  diameter  of  tank  and  any  assumed  height : 
D  X  JfX  62.5  ^  60,000  X  12"  X  $ 

2  4 

from  the  above  the  following  original  tables  have  been  com- 
puted : 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 


IO-FT.  DIAMETER  CYLINDER. 
Circumference,   31.4159  ;    area,    78.5398. 


Height. 

Capacity, 
Gallons. 

Weight, 
Pounds. 

Pressure, 
Pounds. 

Thickness, 
Dec.  In. 

Thickness, 
Frac.  In. 

10 

5,890 

49,087 

3,124 

15 

8,835 

73.631 

4,688 

20 

II,78l 

98,175 

6,250 

25 

14,726 

122,718 

7,812 

30 

17,671 

147,262 

9-374 

35 

2O,6l7 

171,806 

10,938 

40 

23,562 

196,350 

12,500 

45 

26,507 

220,892 

14,062 

50 

29,452 

245,437 

15,624 

55 

32,397 

269,981 

17,188 

60 

35,343 

294,524 

18,750 

65 

38,288 

319,068 

20.312 

70 

41,233 

343,611 

21,876 

.1823 

3/i6 

75 

44,J79 

368,155 

23,438 

•1953 

3/i6 

80 

47,124 

392,699 

25,000 

.2083 

13/64 

85 

50,069 

417,242 

26,562 

.2213 

7/32 

90 

53,oi4 

441,786 

28,124 

•2344 

15/64 

95 

55,96o 

466,330 

29,686 

.2474 

15/64 

100 

58,905 

490,874 

31,250 

.2604 

i/4 

105 

61,850 

515,417 

32,812 

•2751 

9/32 

no 

64,795 

539,961 

34,374 

.2864 

9/32 

"5 

67,741 

564.505 

35,936 

•2995 

19/64 

120 

70,686 

589,048 

37,500 

.3125 

5/i6 

I  I  -FT.   DIAMETER  CYLINDER. 

Circumference,    34.5575;    area,    95.0332. 

10 

7,127 

59,396 

3,438 

15 

10,691 

89,093 

5,156 

20 

14.255 

118,791 

6,874 

25 

17,819 

148,489 

8,594 

30 

21,382 

178,187 

10,312 

35 

24,946 

207,885 

12,032 

40 

28,510 

237,583 

13,750 

45 

32,073 

267,280 

15,468 

50 

35,637 

296,978 

17  188 

55 

39,201 

326,676 

18,906 

60 

42,764 

356,374 

20,624 

65 

46,328 

386,072 

22,344 

.1862 

3/i6 

70 

49,892 

415,770 

24,062 

.2005 

3/i6 

75 

53,456 

445,468 

25.780 

.2146 

7/32 

80 

57,020 

475.165 

27,500 

.2292 

7/32 

85 

60,584 

504,864 

29,218 

•2435 

15/64 

90 

64,147 

534,562 

30,936 

.2578 

1/4 

95 

67,711 

564,259 

32,656 

.2721 

9/32 

100 

7L275 

593,957 

34,374 

.2864 

9/32 

105 

74,839 

623,655 

36,092 

.3007 

19/64 

no 

78,402 

653.353 

37,812 

.3151 

5/i6 

"5 

81,966 

683,051 

39,530 

•  3294 

21/64 

120 

85,530 

712,749 

41,250 

.3438 

11/32 

STABILITY   OF  S7'RUCTURE. 


93 


1 2 -FT.    DIAMETER  CYLINDER. 
Circumference,    37.6991;    area,    113.10. 


Height. 

Capacity, 
Gallons. 

Weight, 
Pounds. 

Pressure, 
Pounds. 

Thickness, 
Dec.  In. 

Thickness, 
Frac.  In. 

IO 

8,483 

70,687 

3,750 

15 

12,724 

106,031 

5,626 

20 

16,965 

I4L375 

7,500 

25 

21,206 

176,719 

9,376 

30 

25,448 

212.063 

11,250 

35 

29,689 

247,406 

13,126 

40 

33-930 

282.750 

15,000 

45 

38,171 

318,094 

16,876 

50 

42,413 

353,438 

18,750 

55 

46,654 

388,781 

20,626 

60 

50,895 

424,125 

22.5OO 

•1875 

3A& 

65 

55,136 

459  469 

24,376 

.  2031 

13/16 

70 

59,378 

494,813 

26,250 

.2187 

7/32 

75 

63,619 

530,156 

28,126 

•2335 

15/64 

80 

67,860 

565,500 

30,000 

.2500 

1/4 

85 

72,101 

600,844 

31,876 

.2656 

17/64 

90 

76,343 

636,187 

33,750 

.2809 

9/32 

95 

80,584 

671,531 

35,626 

.  2969 

19/64 

IOO 

84,825 

706,875 

37,400 

•3117 

5/i6 

105 

89,066 

742,219 

39,376 

.3281 

22/64 

no 

93,308 

777,562 

41,250 

•3437 

11/32 

115 

97,549 

812,906 

43,126 

•3594 

23/64 

120 

101,790 

848,250 

45,000 

•3750 

3/8 

I3-FT.   DIAMETER  CYLINDER. 

Circumference,    40.8407  ;    area,    132.7323. 

IO 

9,955 

82,958 

4,067 

15 

14,932 

124,437 

6,094 

20 

19,910 

165,915 

8,126 

25 

24,887 

207,394 

10,156 

30 

29,865 

248,872 

12,188 

35 

34,842 

290,352 

14,218 

40 

39,820 

331,831 

16,250 

45 

44,797 

373,310 

18,282 

50 

49-775 

414,738 

20,312 

55 

54,752 

456,267 

22,344 

.1862 

3/i6 

60 

59,730 

497,746 

24,374 

•  2031 

13/64 

65 

64,707 

539-225 

26,406 

.2200 

7/32 

70 

69,684 

580,704 

28,438 

.2369 

15/64 

75 

74,662 

622,183 

30,468 

•2538 

1/4 

80 

79.639 

663,661 

32,500 

.2708 

17/64 

85 

84,617 

705,140 

34,532 

.2878 

9/32 

90 

89-594 

746,619 

36,562 

.3046 

19/64 

95 

94,572 

788,098 

38,584 

.3216 

5/i6 

100 

99,549 

829,577 

40,626 

•3384 

21/64 

105 

104,527 

871,056 

42,656 

•3551 

11/32 

no 

109,  504 

912,535 

44,688 

•3724 

3/8 

H5 

114,482 

954.013 

46,718 

.3892 

25/64 

120 

119-459 

995,492 

48,750 

.4062 

13/32 

94 


TOWERS  AND    TANKS  FOR    WATER-WORKS* 


I4-FT.  DIAMETER  CYLINDER. 
Circumference,    43.9823  ;    area,    153.9380. 


Height. 

Capacity, 
Gallons. 

Weight, 
Pounds. 

Pressure, 
Pounds. 

Thickness, 
Dec.  In. 

Thickness, 
Frac.  in. 

IO 

ii,545 

96,211 

4,376 

15 

I7,3i8 

144,317 

6,562 

20 

23,091 

192,423 

8,750 

25 

28,863 

240,528 

10,938 

30 

34,636 

288,634 

13,124 

35 

40,408 

336,739 

15:312 

40 

46,181 

384,845 

17,500 

45 

51,954 

432,951 

19,688 

50 

57,727 

481,056 

21,876 

.1822 

3/i6 

55 

63,499 

529,162 

24,062 

.2005 

13/64 

60 

69,272 

577,268 

26,250 

.2187 

7/32 

65 

75,045 

625,373 

28,438 

.2369 

15/64 

70 

80,817 

673,479 

30,626 

.2588 

i/4 

75 

86,590 

721,584 

32,812 

.2736 

17/64 

80 

92,363 

769,690 

35,000 

.2916 

9/32 

85 

98,135 

817,796 

37,i88 

.3098 

19/64 

90 

103,908 

865,901 

39.376 

.3280 

5/i6 

95 

109,681 

914,007 

41,562 

.3464 

11/32 

100 

115,454 

962,113 

43,748 

.3644 

23/64 

105 

121,226 

1,010,218 

45,936 

.3828 

3/8 

no 

126,999 

1,058,324 

48,124 

.4010 

13/32 

H5 

132,772 

1,106,429 

50,310 

.4192 

27/64 

120 

138,544 

1,155,450 

52,498 

•4374 

7/i6 

I5-FT.  DIAMETER  CYLINDER. 
Circumference,    47.1239  ;    area,    176.7146. 


10 

13  254 

Tio,447 

4,688 

15 

19,880 

165,670 

7,032 

20 

26,507 

220,893 

9,374 

25 

33,134 

276,117 

11,718 

30 

39.761 

331,340 

14,062 

35 

46.388 

386.563 

16,406 

40 

53,014 

441,786 

18,750 

45 

59.641 

497,010 

21,094 

50 

66,268 

552,233 

23,436 

•1953 

3/16 

55 

72,895 

607,456 

25,78o 

.2146 

13/64 

60 

79,522 

662,680 

28,124 

•2344 

15/64 

65 

86,148 

717,903 

30,468 

•2538 

1/4 

70 

92,775 

773.126 

32,812 

.2730 

9/32 

75 

99,402 

828,350 

35,156 

.2930 

9/32 

80 

106,029 

883,573 

37,500 

.3124 

5/i6 

85 

112,656 

938,796 

39,844 

.3320 

21/64 

90 

119,282 

994,020 

42,188 

.3516 

11/32 

95 

125,909 

,049,243 

44,532 

.3710 

3/8 

100 

132,536 

,104,466 

46.874 

.3908 

25/64 

105 

139,163 

,159,690 

49,218 

.4100 

13/32 

no 

145.789 

,214,913 

51,562 

.4296 

27/64 

H5 

152,416 

,270,136 

53,906 

.4492 

29/64 

120 

159,043 

,325,359 

56,250 

.4688 

15/32 

STABILITY  OF  STRUCTURE. 


95 


I6-FT.  DIAMETER  CYLINDER. 
Circumference,    50.2655;    area,    201.0619. 


Height. 

Capacity, 
Gallons. 

Weight, 
Pounds. 

Pressure. 
Pounds. 

Thickness, 
Dec.  In. 

Thickness, 
Frac.  In. 

IO 

15,080 

125,664 

5,000 

15 

22,619 

188,495 

7,500 

20 

30,160 

251,327 

10,000 

25 

37,699 

314,159 

12,500 

30 

45,239 

376,991 

15,000 

35 

52,779 

439,823 

17,500 

40 

60,319 

502,655 

20,000 

45 

67,858 

565,486 

22,500 

.1875 

3/i6 

50 

75,398 

628,318 

25,000 

.2083 

13/64 

55 

82,938 

691,150 

27,500 

.2291 

7/32 

60 

90,478 

753,982 

30,000 

.2500 

1/4 

65 

98,018 

816,814 

32,500 

.2708 

17/64 

70 

105,557 

879,646 

35,000 

.2916 

/ 

9/32 

75 

113,097 

942,478 

37,500 

-3I24 

5/i6 

80 

120,637 

,005,309 

40  ,000 

•3332 

21/64 

85 

128,177 

,068,141 

42,500 

•3540 

11/32 

90 

135,717 

,130,973 

45,000 

•3750 

3/8 

95 

143,257 

,193,805 

47,500 

.3960 

25/64 

IOO 

150,796 

,256,637 

50,000 

.4166 

13/32 

105 

158,336 

,319,469 

52,500 

•4374 

7/16 

no 

165,876 

,382,300 

55,ooo 

.4584 

29/64 

"5 

173,416 

,445,132 

57,500 

.4792 

15/32 

120 

180,956 

,507,964 

60,000 

.5000 

1/2 

I7-FT.  DIAMETER  CYLINDER. 

Circumference,  53.4071;  area,  226.9800. 

10 

17,023 

141,862 

5,312 

15 

25,535 

212,794 

7,968 

20 

34,047 

283,725 

10,624 

25 

42,559 

354,656 

13,282 

30 

51,070 

425,587 

15.938 

35 

59,582 

496,519 

18,584 

40 

68,094 

567,450 

21,250 

45 

76,606 

638,381 

23,906 

.1992 

3/16 

50 

85,H7 

709,312 

26,562 

.2213 

7/32 

55 

93,629 

780,244 

29,218 

•2434 

1/4 

60 

102,141 

851,175 

31,874 

.2656 

17/64 

65 

110,653 

922,106 

34.532 

.2878 

9/32 

70 

119,164 

993,037 

37,i88 

.3098 

5/i6 

75 

127,676 

,063,969 

39,844 

•  3320 

21/64 

80 

136,188 

,134,900 

42,500 

•3544 

11/32 

85 

144,699 

,205,831 

45,156 

•3762 

3/8 

90 

153,211 

,276,762 

67,812 

.3984 

25/64 

95 

161,723 

,347,694 

50,468 

.4206 

27/64 

IOO 

170,235 

,418,625 

53,124 

.4426 

7/16 

105 

178,747 

,489,556 

55,782 

.4648 

15/32 

no 

187,258 

,560,488 

58,438 

.4874 

31/64 

H5 

195,770 

,631,419 

61,094 

.5090 

1/2 

120 

204,282 

,702,350 

63,750 

.5278 

17/32 

96 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 


I8-FT.  DIAMETER  CYLINDER. 
Circumference,    56.5487;    area,    254.4690. 


Height. 

Capacity, 
Gallons. 

Weight, 
Pounds. 

Pressure, 
Pounds. 

Thickness, 
Dec.  In. 

Thickness, 
Frac.  In. 

IO 

19,085 

159,043 

5,625 

15 

28,628 

238,565 

8,438 

20 

38,170 

318,086 

11,250 

25 

47,713 

397,608 

14,062 

30 

57,255 

477,129 

16,876 

35 

66,798 

556,651 

19,686 

40 

76?34I 

636,172 

22,5OO 

.1875 

3/i6 

45 

85,883 

715,694 

25,312 

.2109 

7/32 

50 

95,426 

795,215 

28,124 

•2344 

15/64 

55 

104,968 

874,737 

33,936 

•2578 

i/4 

60 

114,511 

954-258 

33,750 

.2812 

9/32 

65 

124,054 

,033,780 

36,562 

.3040 

5/i6 

70 

133,596 

,113.302 

39,374 

.3280 

21/64 

75 

143,139 

,192,823 

42,186 

•3516 

11/32 

80 

152,681 

,272,345 

45,ooo 

•3758 

3/8 

85 

162,224 

,351,866 

47,812 

•3984 

25/64 

90 

171,766 

,431,388 

50,624 

.4218 

27/64 

95 

181,309 

,510,910 

53,436 

•4452 

7/16 

100 

190,852 

,590,431 

56,250 

.4688 

15/32 

105 

200,394 

,669,953 

59,062 

.4922 

31/64 

no 

209,937 

,749.474 

61,874 

•5156 

1/2 

115 

219,479 

,828,996 

64,874 

•5409 

35/64 

1  20 

229,022 

,908,517 

67,500 

.5626 

9/16 

IQ-FT.  DIAMETER   CYLINDER. 
Circumference,    59.6903;    area,    283.5287. 


10 

21,265 

177,205 

5,968 

15 

31,897 

265,808 

8,906 

20 

42,529 

354,411 

n,875 

25 

53,162 

443,014 

14,844 

30 

63,794 

53I,6l6 

17,812 

35 

74,426 

620.219 

20,781 

40 

85,059 

708  822 

23.750 

.1896 

3/16 

45 

95,691 

797.424 

26,718 

.2226 

7/32 

50 

106,323 

886,023 

29,687 

.2472 

15/64 

55 

116,956 

974  630 

32,656 

.2721 

17/64 

60 

127,588 

,063,232 

35,625 

.2969 

19/64 

65 

138,220 

,151,835 

38,594 

.3216 

21/64 

70 

148.852 

,240,438 

41,562 

.3463 

11/32 

75 

159,485 

,329,°4i 

44,532 

-37II 

3/8 

80 

170,117 

,417,644 

47>  500 

•3958 

25/64 

85 

180,750 

,506,246 

50,468 

.4205 

13/32 

90 

191,382 

,594,849 

53,437 

•4453 

7/i6 

95 

2O2  OI4 

,683,452 

56,406 

.4700 

15/32 

IOO 

212,646 

,772,054 

59,375 

.4948 

1/2 

105 

223,279 

,860,657 

62,344 

.5195 

33/64 

no 

233,911 

,949,260 

65,312 

•5443 

35/64 

H5 

244,543 

2,037,862 

68,281 

.5690 

9/i6 

120 

255,176 

2,126,465 

71,250 

•5937 

19/32 

STABILI7'Y   OF  STRUCTURE. 


97 


20-FT.  DIAMETER   CYLINDER. 
Circumference,    62.8318;    area,    314.1593. 


Height. 

Capacity, 
Gallons. 

Weight, 
Pounds. 

Pressure, 
Pounds. 

Thickness, 
Dec.  In. 

Thickness, 
Frac.  In. 

IO 

23,562 

196,350 

6,250 

15 

35,343 

294,524 

9,375 

20 

47,124 

392,700 

12,500 

25 

58,905 

490,874 

15,625 

30 

70,686 

589,048 

18,750 

35 

82,467 

687,223 

21,875 

.1823 

3/16 

40 

94  248 

785,398 

25,000 

.2083 

13/64 

45 

106,029 

883,573 

28,125 

•2344 

15/64 

50 

117,810 

981,748 

31,250 

.2604 

17/64 

55 

129,591 

1,079,923 

34,375 

.2865 

9/32 

60 

141,372 

1,178,097 

37,500 

•3125 

5/16 

65 

153,153 

1,276,272 

40,625 

•3385 

21/64 

70 

164,934 

1,374,447 

43,750 

.3646 

23/64 

75 

176,715 

1,472,622 

46,875 

.3906 

25/64 

80 

188,496 

1,570,796 

50,000 

.4166 

13/32 

85 

200,277 

1,668,971 

53,125 

.4427 

7/i6 

90 

212,058 

1,767,146 

56,250 

.4688 

15/32 

95 

223,839 

1,865,321 

59-375 

.4948 

31/64 

100 

235,619 

1,963,496 

62,500 

.5208 

1/2 

105 

247,400 

2,061,670 

65,625 

•5469 

35/64 

no 

259,181 

2,159,845 

68,750 

.5729 

37/64 

"5 

270,962 

2,258,020 

71,875 

.5989 

19/32 

120 

282,743 

2,356,194 

75,000 

.6250 

5/8 

2  I -FT.  DIAMETER   CYLINDER. 
Circumference,    65.9735;    area,    346.3606. 


IO 

25,977 

216,475 

6,563 

15 

38,966 

324,713 

9,844 

20 

51,954 

432,951 

13,126 

25 

64,943 

541,188 

16,406 

30 

77,932 

649,426 

19,688 

35 

90,920 

757,664 

22,969 

.1914 

3/16 

40 

103,908 

865,902 

26,250 

.2187 

7/32 

45 

116,897 

974-139 

29,53i 

.2461 

15/64 

50 

1  29,8*85 

1,082,377 

32,812 

•2734 

17/64 

55 

142,874 

1,190,615 

36,094 

.3008 

19/64 

60 

155,862 

1,298,852 

39,375 

.3281 

21/64 

65 

168,151 

1,407,090 

42,656 

•3554 

23/64 

70 

181,839 

1,515,328 

45,938 

.3828 

3/8 

75 

194,828 

1,623,565 

49,219 

.4101 

13/32 

80 

207,816 

1,731-803 

52.500 

•4375 

7/16 

85 

220,805 

1,840,040 

55,78i 

.4648 

15/32 

90 

233,793 

1,948,278 

59,062 

.4922 

1/2 

95 

246,782 

2,056,516 

62,344 

.5195 

33/64 

100 

259,770 

2,164,754 

65,625 

.5469 

35/64 

105 

272,759 

2,272,991 

68,906 

•5742 

37/64 

no 

285,747 

2,381,229 

72,188 

•  6015 

39/64 

"5 

298,736 

2,489,467 

75,469 

.6289 

5/8 

120 

3",724 

2,597,704 

78,750 

.6562 

21/32 

TOWERS  AND    TANKS  FOR    WATER-WORKS. 


22-FT.   DIAMETER    CYLINDER. 
Circumference,    69.1150;    area,    380.1327. 


Height. 

Capacity, 
Gallons. 

Weight, 
Pounds. 

Pressure, 
Pounds. 

Thickness, 
Dec.  In. 

Thickness, 
Frac.  In. 

10 

28,510 

237.583 

6,875 

15 

42,765 

356,374 

IO,3I2 

20 

57,020 

475,166 

13,750 

25 

71,275 

593,957 

17,187 

30 

85,530 

712,749 

20,625 

35 

99.785 

831,540 

24,063 

.2005 

3/i6 

40 

114  040 

950,332 

27,500 

.2292 

7/32 

45 

128  295 

,069  123 

30,937 

.2578 

1/4 

50 

142,550 

,187,915 

34,375 

.2865 

9/32 

55 

156,805 

,306,706 

37,812 

•3151 

5/16 

60 

171,060 

,425,498 

41,250 

•3438 

11/32 

65 

185,315 

.544,289 

44,687 

-3724 

3/8 

70 

199,570 

,663,081 

48,125 

.4010 

13/32 

75 

213.825 

,781,872 

51,562 

.4297 

7/16 

80 

228,080 

,900,663 

55,000 

•4583 

15/32 

85 

242,335 

2,019,455 

58,437 

.4869 

1/2 

90 

256,590 

2,138,246 

61,875 

.5156 

33/64 

95 

270,845 

2,257,038 

65,312 

•5443 

35/64 

100 

285,100 

2,375.830 

68,750 

•5729 

9/1  6 

105 

299,354 

2,494,621 

72,187 

.6015 

39/64 

no 

313.609 

2,613,412 

75,625 

.6402 

41/64 

115 

327,864 

2,732,204 

79,062 

.6588 

21/32 

1  20 

342,119 

2,850,996 

82,500 

.6875 

11/16 

23-FT.  DIAMETER    CYLINDER. 


Circumference,  72.2566  ;  area,  415.4756. 

10 

3I,l6l 

259-672 

7,187 

15 

46,741 

389,508 

10,781 

20 

62,321 

519,344 

14  375 

25 

77,902 

649,^81 

17,968 

30 

93,482 

779,oi6 

21,562 

35 

109,062 

908,853 

25.156 

.2096 

3/1* 

40 

124,643 

,038,689 

28,750 

.2396 

15/64 

45 

I4'J,223 

,168,525 

32,343 

.2695 

9/32 

50 

155,803 

,298,361 

35,937 

•2995 

5/16 

55 

I7L384 

,428,197 

39.531 

.3294 

11/32 

60 

186,964 

,558,033 

43,125 

•3594 

23/64 

65 

202,544 

,687,869 

46,719 

.3893 

25/64 

70 

218,125 

,817,706 

50,312 

•4193 

27/64 

75 

233,705 

,947.542 

53,906 

.4492 

29/64 

80 

249,285 

2,077,376 

57.500 

•4792 

31/64 

85 

264,866 

2,207,214 

61,093 

.5091 

1/2 

90 

280,446 

2,337.050 

64,687 

•5390 

17/32 

95 

296,026 

2,466,886 

68,281 

.5690 

9/16 

100 

311,607 

2,596,722 

71,875 

•5989 

19/32 

105 

327,187 

2,726,558 

75,468 

.6289 

5/8 

no 

342,767 

2,856,395 

79,062 

.6589 

21/32 

H5 

358,348 

2,986,231 

82,656 

.6888 

11/16 

120 

373,928 

3,116,067 

86,250 

.7187 

23/32 

STABILITY   OF  STRUCTURE. 

24-FT.  DIAMETER  CYLINDER. 
Circumference,  75.3982  ;    area,    452.3893. 


99 


Height. 

Capacity, 
Gallons. 

Weight, 
Pounds. 

Pressure, 
Pounds. 

Thickness, 
Dec.  In. 

Thickness, 
Frac.  In. 

10 

33,929 

282,743 

7,500 

15 

50,894 

424,H5 

11,250 

20 

67,858 

565,436 

15,000 

25 

84,823 

706,858 

18,750 

30 

111,788 

848,230 

22,500 

.1875 

3/16 

35 

118,752 

989,602 

26,250 

.2187 

7/32 

40 

135,717 

1,130,973 

3O,OOO 

.2500 

1/4 

45 

152,682 

,272,345 

33,750 

.2812 

9/32 

50 

169,646 

,413,716 

37.500 

•3125 

5/16 

55 

186,610 

,555-088 

4r,250 

•3437 

11/32 

60 

203,575 

,696,460 

45,000 

•3750 

3/8 

65 

220,540 

,837,831 

48,750 

•  4063 

13/32 

70 

237*504 

1,979,203 

52,500 

•4375 

7/16 

75 

254,469 

2,120,575 

56,250 

.4687 

15/32 

80 

271,434 

2,261,947 

60,000 

.5000 

1/2 

85 

288,398 

2,403,318 

63,750 

•5313 

17/32 

90 

305,363 

2,544,690 

67,500 

•  5625 

9/16 

95 

322,327 

2,686,061 

71,250 

.      .5938 

19/32 

TOO 

339,292 

2,827,433 

75,ooo 

.6250 

5/8 

105 

356,256 

2,968,805 

78.750 

.6563 

21/32 

no 

373,221 

3,110,176 

82,500 

.6875 

11/16 

"5 

390,186 

3,251,548 

86,250 

.7187 

23/32 

120 

407,150 

3,392,920 

90,000 

•7500 

3/4 

2  5 -FT.  DIAMETER   CYLINDER. 
Circumference,    78.5398  ;    area,    490.8739. 


IO 

36,815 

306,796 

7,812 

15 

55,223 

460,194 

11,719 

20 

73,631 

6i3,592 

15,625 

25 

92,039 

766,990 

I9,53i 

30 

110,447 

920,389 

23,437 

.1871 

3/16 

35 

128,854 

1,073  787 

27,344 

,2279 

15/64 

40 

147,262 

1,227,185 

31,250 

.2604 

17/64 

45 

165,670 

,380,583 

35,156 

.2929 

19/64 

50 

184,077 

,533,981 

39,062 

3255 

21/64 

55 

202,485 

,687,379 

42,969 

•3581 

23/64 

60 

220,893 

,840,777 

46,875 

.3906 

25/64 

65 

239,301 

,994,175 

50,781 

.4232 

27/64 

70 

257,709 

2,147-573 

54,687 

•4558 

29/64 

75 

276,117 

2,300,971 

58,594 

.4883 

31/64 

80 

294,524 

2,454-370 

62,500 

.5208 

17/32 

85 

312,932 

2,607,768 

66,406 

•5534 

9/16 

90 

331,340 

2,761.166 

70,312 

.5859 

19/32 

95 

349,748 

2,914-563 

74.219 

.6185 

5/8 

TOO 

105 

no 

368,155 
386,563 
404,971 

3,067,962 
3,221.360 

3,374,758 

78,125 
82,031 
85,937 

.6510 
.6836 
.7161 

21/32 
11/16 
23/32 

115 

423,379 

3,528,156 

89,844 

.7487 

3/4 

1  20 

441,786 

3,681.554 

93,750 

.7812 

25/32 

CHAPTER  V. 

MECHANICAL    PRINCIPLES. 

IN  the  previous  chapter  it  has  been  shown  that  the  appli- 
cation of  force  as  tension,  compression,  or  shear,  produces 
strain  among  the  particles  of  which  the  body  consists,  and  that 
this  external  pressure  is  resisted  by  the  cohesive  force  of  its 
fibres ;  also  that  the  internal  resistance  of  the  particles  depends 
upon  their  number  and  their  arrangement  in  the  cross-section. 
When  weight  or  pressure  is  applied  to  such  body  as  a  beam 
or  girder,  two  opposing  forces  are  set  in  motion;  one  tending 
to  cause  rupture  or  the  breaking  of  the  beam  through  its  cross- 
section,  and  the  other  exerting  an  opposing  force  of  the  fibre 
resistance  depending  in  effect  upon  arrangement  and  tenacity. 
The  tendency  of  the  load  applied  to  the  beam  is  to  produce 
"flexure"  or  bending,  straining  the  fibres  on  the  under  side 
of  the  beam  or  producing  tension  among  them,  and  compress- 
ing correspondingly  the  upper  or  outside  fibres,  both  directly 
as  their  distance  from  the  outer  sides  toward  the  centre  of  the 
beam.  The  strain  which  taxes  to  the  maximum  those  most 
remote  fibres  from  the  central  line,  both  by  tension  and  com- 
pression, is  gradually  neutralized  as  the  strain  of  tension  and 
compression  approach  each  other,  and  at  the  line  of  the  cross- 
section  where  these  two  opposing  forces  meet,  the  fibres  are  at 
rest  as  regards  each  other,  or  are  said  to  be  in  equilibrium,  and 
at  that  line  the  fibres  are  neither  under  tension  nor  compression. 

100 


MECHANICAL    PRINCIPLES.  IOI 

The  line  through  the  cross-section  of  any  beam  where  the 
fibres  are  not  strained  is  termed  the  "neutral  axis"  of  the 
beam.  In  the  case  of  all  vertical  loads,  this  neutral  axis  exists 
arid  passes  through  the  centre  of  gravity  of  the  beam  cross- 
section  parallel  to  the  top  and  bottom  faces  of  the  beam. 

Bending  and  Resisting  Moments. — The  effect  of  any  ver- 
tical load,  acting  through  the  centre  of  gravity  of  the  beam  to 
produce  flexure,  is  the  amount  of  the  load  sustained  and  the 
point  of  application,  or  its  leverage,  as  well  the  (<  bending 
moment"  M  at  any  cross-section  of  a  beam,  or  the  algebraic 
sum  of  the  vertical  forces  on  the  left  or  right  of  the  section, 
where  the  tendency  of  the  forces  is  to  cause  motion  by  rota- 
tion around  that  point.  The  maximum  bending  moment 
occurs,  of  course,  where  the  beam  is  most  greatly  strained. 
Without  demonstration,  the  bending  moment  of  a  beam, 
uniformly  loaded  and  supported  at  both  ends,  M=  \Wl; 
where  W  =.  the  total  load  and  /  its  leverage. 

The  resistance  offered  by  the  fibres  and  their  arrangement 
to  the  effects  of  the  applied  load  is  determined  by  the  "  re- 
sisting moment,"  R,  of  the  beam,  and  is  found  by  obtain- 
ing the  algebraic  sum  of  all  the' moments  of  the  horizontal 
stresses  producing  tension  and  compression  of  the  fibres,  act- 
ing in  opposite  directions  but  parallel  to  each  other.  These 
moments  are  determined,  with  respect  to  the  neutral  axis,  by 
adding  together  or  summing  up  algebraically  all  the  moments 
of  all  the  unit  stresses  acting  upon  all  the  elementary  areas 
of  which  the  cross-section  consists. 

When  this  value  equals  that  of  the  applied  weight  when 
multiplied  by  its  leverage  of  action,  called  the  "moment  of 
rupture,"  or  M,  we  have  the  equation,  R  =  M,  indicating 
equilibrium  between  the  forces  tending  to  cause  rupture  and 
those  which  offer  resistance  to  the  former  forces. 

Moment  of  Inertia. — In  the  consideration  and  design  of 
beams,  the  effect  of  the  shape  or  cross-section  of  the  beam  has 
to  be  taken  into  account  and  is  analyzed  by  the  aid  of  a 


102  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

quantity  termed  the  "moment  of  inertia,"  /,  which,  referred 
to  the  neutral  axis  of  the  beam,  is  the  product  of  the  square 
of  the  distance  from  that  axis  to  all  the  elementary  areas  of 
the  cross-section,  and  its  value  is  determined  by  summing  up 
the  product  of  the  elementary  areas,  multiplied  by  the  square 
of  their  distances  from  the  neutral  axis,  or  solving  2az*  where 
2  represents  the  summation,  a  the  elementary  area,  and  z  its 
distance  from  the  neutral  axis. 

Without  demonstration,  the  resisting  moment,  R,  of  a 
beam  is  determined  by  dividing  the  moment  of  inertia,  /, 
by  the  distance,  as  c,  from  the  neutral  axis  to  the  extreme 

fibres;  therefore  the  formula,  R  =  -. 

c 

Modulus  of  Elasticity. — As  has  been  said,  not  only  does 
the  cross-section  of  the  beam,  representing  the  arrangement 
of  the  fibres,  have  to  be  taken  into  consideration  in  determin- 
ing the  resistance  offered  by  a  given  form  to  an  external  force, 
but  the  tenacity  of  those  fibres  or  their  cohesive  force,  and 
this  last  consideration  deals  with  the  relative  ability  to  resist 
"  elastic  deformation  "  to  the  point  of  "  ultimate  elongation  " 
and  rupture.  Provided  none  of  the  stresses  exceed  the  "  elastic 
limit  "  of  the  material,  the  elongation  and  deflection  of  beams 
can  be  computed. 

The  letter  E  is  generally  taken  to  represent  the  "mod- 
ulus of  elasticity"  or  the  '  *  coefficient  of  elasticity,"  rep- 
resentative terms  expressing  the  ratio  of  "unit  stress"  to 
"  unit  deformation,"  and  to  be  found  by  dividing  the  unit 
stress,  as  S,  representing  say,  the  stress  in  pounds  per 
square  inch,  by  the  unit  of  elongation  which,  by  experiment, 
has  been  found  to  follow  the  application  of  stress  on  different 

5 

materials,  as  s',   hence,  E  =  — . 

Under  tension,  and  compression,  experiment  has  deter- 
mined that  the  coefficient  or  modulus  R  is  practically  the 


MECHANICAL   PRINCIPLES.  103 

same,  while  for  shear  stress,  it  is  generally  assumed  at  one- 
third  less.  It  is  further  generally  assumed  that  the  stress 
under  tension  and  compression  when  the  elastic  limit  is  reached 
is  about  six-tenths  of  the  ultimate  tenacity. 

According  to  William  Kent,  A.  M.  M.  E.,  one  of  the  most 
recognized  authorities  on  mechanical  questions,  the  following 
are  the 

MODULI    OF   ELASTICITY    FOR   IRON   AND    STEEL. 

Cast  iron 12,000,000  to  27,000,000  (?) 

Wrought  iron...  .22,000,000  to  29,000,000 

Steel 26,000,000  to  32,000,000. 

Quoting  from  "  Kent's  Pocket  Book  "  :  "  The  maximum 
figures  given  by  many  writers  for  iron  and  steel,  viz., 
40,000,000  and  42,000,000,  are  undoubtedly  erroneous.  .  .  . 
The  modulus  of  elasticity  of  steel  (within  the  elastic  limit)  is 
remarkably  constant,  notwithstanding  great  variations  in 
chemical  analysis,  temper,  etc.  It  rarely  is  found  below 
28,000,000  or  above  31,000,000.  It  is  generally  taken  at 
30,000,000  in  engineering  calculations." 

The  values  given  above  are  generally  approximated  as 
follows : 

Cast  iron 15,000,000  pounds  per  square  inch 

Wrought  iron.. 2 5, 000,000        "  "         il          " 

Steel   30,000,000        "  "         "          " 

When  under  tension  or  compression  steel  will  stretch  or  shorten 

I 
30,000,000 

part  of  its  normal  length  for  every  pound  per  sectional  inch 
in  change  of  load. 

The  tendency  of  columns  or  struts  under  load  is  to  fail  by 
both  compression  and  flexure,  or  bending,  the  column  yzeld- 


IO4  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

ing  to  the  applied  load,  and  deflecting  laterally ;  the  longer 
the  column  the  greater  the  tendency  to  this  lateral  deflection 
or  bending,  and  the  greater  the  stresses  upon  the  fibres  of  the 
concave  side.  The  combined  stress  is  very  complex  and 
difficult  of  demonstration,  but  it  is  pretty  well  established  that 
the  stress  produced  by  such  deflection  increases  directly  as  the 
square  of  the  length  of  the  beam. 

In  the  discussion  of  columns,  a  quantity  called  the  "  radius 
of  gyration  "  of  the  cross-section  is  an  important  factor  in  cal- 
culations, and,  in  the  determination  of  the  strength  of  a 
column  or  strut,  represents  the  effect  of  the  form  of  the 
column  which  is  expressed  by  the  square  of  the  radius  of 
gyration,  or  the  moment  of  inertia  of  the  section  divided  by  its 

7-r1 

area,  or -. . 

A 

Radius  of  Gyration. — In  the  discussion  of  columns,  a  quantity 
called  the  "radius  of  gyration"  is  an  important  factor  in  the 
determination  of  the  strength  of  columns  to  resist  the  applied 
stresses.  This  quantity  has  been  denned  as  "that  quantity 
whose  square  is  equal  to  the  moment  of  inertia  of  the  cross- 
section  divided  by  its  area,  or 

r»=- 
A 

is  the  expression  by  which  r2  is  to  be  computed. 

"  It  should  be  observed  that  r  has  no  connection  with  gyra- 
tion, as  /  has  no  connection  with  inertia,  in  the  case  of  sections 
of  beams  and  columns. 

"  Radius  of  gyration  is  merely  a  technical  name,  which  has- 
unfortunately  come  into  use,  to  denote  the  square  root  of  the 

quantity  -7." 

In  the  numerous  publications  by  the  larger  steel  manufac- 
tories, the  radius  of  gyration,  the  moment  of  inertia,  and  the  other 
elements  of  standard  shapes  have  been  conveniently  tabulated 


MECHANICAL   PRINCIPLES. 

and  are  so  generally  accurate  that  it  is  seldom  necessary  to  cal- 
culate these  values  from  formulae. 

For  the  determination  of  the  ultimate  load  of  columns 
numerous  formulae  have  been  developed,  predicated  upon,  or 
modifications  of,  two  original  and  well-known  formulae,  those 
of  Rankine  and  of  Gordon.  The  following  is 

RANKINE'S  FORMULA  FOR  COLUMNS. 

P        S 

=      —  5,  where 


A=  section  area; 

P  =  load  on  vertical  column; 

S  =  maximum  unit  stress; 
r=  radius  of  gyration; 
/=  length  of  column; 

q  =  coefficient,  depending  upon  kind  of  material  and  the 
arrangement  of  the  ends.  (Note.  Where  steel  is  used,  and  botrt 
ends  fixed,  q  =  l  --  25,000.) 

The  Gordon  Formula  for  Strength  of  Columns.  —  Notwith- 
standing steel  made  into  columns  has  shown  a  working  value 
of  20%  in  excess  of  iron  up  to  lengths  of  90  radii  of  gyration, 
it  is  only  recently  that  this  allowance  was  made,  some  mills  still 
retaining  without  modification  the  formula  invented  by  Lewis 
Gordon  in  1840,  after  tests  made  before  the  British  Board  of 
Trade,  and  which  is  as  follows. 

ULTIMATE    STRENGTH  OF   COLUMNS. 

40,000 

Square  beanng  =      -  . 


36,ooor2 

For  safe  resistance:  quiescent  loads,  as  for  a  building,  divide  by  4. 
For   safe   resistance:    moving   loads,  as  in  bridges,  divide  by  5. 


io6 


TOWERS  AND    TANKS  FOR    WATER-WORKS, 


In  the  above  formula,  the  constant,  12,  is  to  reduce  the  length  /, 
in  feet,  to  inches ;  r  represents  the  least  radius  of  gyration.  From 
Gordon's  formula,  the  working  value  of  the  metal  per  square 
inch  of  section  for  columns  of  varying  length  is  found;  this,  multi- 
plied by  the  area  of  the  section,  gives  the  ultimate  load. 

To  apply  the  Gordon  formula,  the  length  and  section  of 
the  column  must  be  known  or  assumed,  and  from  the  area  of 
the  cross-section  the  element  r  can  be  found  by  dividing  the 
moment  of  inertia  of  the  shape  by  its  area,  as  has  been  shown ; 
but  in  general  r  can  be  more  conveniently  found  from  any  of 
the  usual  handbooks.  In  order  to  further  lessen  the  computa- 
tions, the  following  original  table  is  given. 

STRENGTH    OF    STEEL    COLUMNS— BASED    UPON    GORDON'S 

FORMULA. 

Factor  of  safety  of  4  used  in  table.    20  per  cent  greater  value  assumed  for  steel  than  for 
iron  columns. 

/  =  length  of  column  in  feet. 
r  =  least  radius  of  gyration. 
5  =  safe  value  of  material  per  square  inch  of  metal  section. 


I 

r 

S 

I 

r 

5 

l_ 

r 

5 

2  O.  .  .  .  .  . 

11810 

s!.o 

....  10908 

8  o 

OC  C4, 

2  2  

.  11774 

s".2.  . 

10826 

8  2   . 

04^6 

2  A 

1  1730 

c"  A 

10746 

8  4 

V45" 
Q-2  en 

2  6 

1168? 

5  6 

10662 

8  6 

9260 

2  8 

n6ic 

e.g 

10^78 

8  8 

9162 

3O 

11586 

6  o 

.  i  0400 

90 

9062 

32  . 

11582 

6  2 

.  .  I  0400 

92 

8964 

34  . 

.  .  11468 

6  4  

....  10310 

04. 

...  .  8864 

•?  6.  . 

11408 

6.6  

....  10218 

0.6  . 

.  8768 

is.. 

11346 

6.8  

....  10124 

9.8  

8670 

40 

1  1  276 

7  O 

I  OO3  2 

IO  O 

8s  70 

42 

11208 

7  2 

00^8 

IO  2 

8"T4 

4   A 

in  ^6 

7  4 

9842 

10  4 

...  8^76 

4.  6  . 

11060 

7.6  . 

0746 

10,8  

8180 

The  table  is  based  upon  the  Gordon  formula  for  iron  columns 
with  a  higher  value  of  20  per  cent,  which  from  experiment  has 


ME  CHA  NIC  A  L   PRINCIPL  ES. 


107 


70 


40 


30 


20 


12,000  Ibs.         11,000"  10,000"  9,000" 8,000"    r        7,000"  6,000"  5,000  Ibs. 


70' 


CO' 


50' 


12,000  Ibs.        11,000' 


10,000' 


9,000' 
P 


8,000» 


7,000» 


6,000" 


5,000  Ibs. 


DIAGRAM  or  STRAIGHT- LINE  COMPRESSION  FORMULAS. 

Formula:  P=  12,500—  500  (!-s-r), 
P  —  compression  in  pounds  per  square  inch, 
/  =  unsupported  length  of  member  in  feet, 
r  =  radius  of  gyration  in  inches. 

Explanation.  Find  the  required  r  on  the  line  r  —  r,  then  follow  the  diagonal  which 
crosses  at  that  point,  until  it  crosses  the  line  representing  the  required  /  (read  at  the  sides 
of  the  diagram).  The  vertical  line  through  this  intersection  represents  P  (read  at  the  top 
and  bottom  of  diagram).  Diagonal  lines  representing  r  are  drawn  at  each  half-inch  only. 
Lines  for  intermediate  values  may  be  drawn  in,  or  a  ruler  or  thread  used  to  indicate  them 


I08  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

been  determined  as  applicable  to  steel  columns  less  than  90 
radii. 

To  use  the  table,  divide  the  length  of  the  column  in  feet  by 
the  least  radius  of  gyration  of  the  section,  and  from  the  corre- 
sponding ratio  of  the  table  find  the  unit  strength  of  the  material 
in  pounds,  which,  multiplied  by  the  combined  area  of  the  shape, 
will  give  the  safe  load  in  pounds  for  a  column  of  the  required 
length  and  cross-section. 

Of  late  numerous  straight-line  compression  formulas  have 
been  presented,  and  diagrams  constructed  from  same  have  sprung 
into  common  use.  Herewith  is  reproduced  one  prepared  by 
Mr.  O.  W.  Childs,  C.E.,  and  published  in  January,  1900,  by  the 
Engineering  News. 


CHAPTER  VI. 
THE  STRESSES    IN    A    STEEL    WATER-TOWER.* 

IT  is  the  purpose  of  this  chapter  to  collect  and  reduce  to 
convenient  working  form  the  formulae  required  in  solving  the 
stresses  in  a  steel  water-tower.  A  water-tower  is  understood 
to  be  a  water-tank  and  the  tower  or  trestle  supporting  it.  The 
tower  may  have  three  or  more  posts.  It  is  assumed  that  the 
posts  are  spaced  equidistant,  i.e.,  at  the  corners  of  a  regular 
polygon.  The  tank  is  cylindrical.  Its  bottom  may  be  flat, 
conical,  or  spherical.  The  flat  bottom  is  rarely  used  in  important 
structures  and  will  not  be  considered. 

The  forces  acting  on  a  water-tower  are  gravity  and  wind 
pressure.  These  forces  or  loads  must  be  transmitted  by  the 
structure  from  the  points  of  application  to  the  points  of  support 
•or  foundations.  In  the  discussion  following,  the  loads  will  be 
traced  from  their  points  of  application  to  the  foundations,  and 
the  resulting  stresses  in  the  successive  members  or  parts  of  the 
structure  determined.  Secondary  stresses,  i.e.,  local  stresses 
resulting  from  details  of  construction,  will  not  be  considered. 

GRAVITY    STRESSES. 

The  force  of  gravity  acting  on  a  water-tower  equals  the 
weight  of  the  structure  plus  the  weight  of  the  water  supported 
by  it.  The  weight  of  the  proposed  water-tower  may  be  deter- 

*  By  H.  J.  Burt.  Revised  from  paper  in  The  Technograph,  No.  16,  1901-2, 
University  of  Illinois. 

109 


no 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 


mined,  accurately  enough  for  purposes  of  design,  by  compari- 
son with  the  design  of  a  similar  structure,  if  such  is  available 


FIG.  18. 


or  from  the  tentative  designs  of  the  several  parts  as  the  weights 
of  those  parts  are  required.     The  weight  of  the  water  can  be  de- 


• 

THE   STRESSES  IN  A    STEEL    WATER-TOWER.         Ill 

termined  readily  from  the  cubical  contents  of  the  tank,  using 
the  following  values: 

i  cubic  foot  of  water  weighs 62.5  pounds 

i  gallon  of  water  weighs 8.33  pounds 

i  cubic  foot  contains 7.48  gallons 

This  weight  is  correct  within  one-half  of  one  per  cent,  and 
errs  on  the  side  of  safety. 

Nomenclature.— Fig.  18  illustrates  the  nomenclature  of  di- 
mensions used  in  the  formulae. 

H  equals  the  depth  or  head  of  water  in  feet  at  the  point  under 
consideration. 

p  equals  the  hydrostatic  pressure  in  pounds  per  square  inch, 
hence  equals  0.434^". 

W  equals  the  total  load  in  pounds  supported  by  the  section 
or  member  under  consideration. 

Dimensions  in  feet  are  expressed  by  capital  letters,  and  in 
inches  by  small  letters. 

Capacity  0}  Cylinder. 

x&A 

Capacity  in  cubic  feet  =   . 

Capacity  in  gallons      =  -      -  X  7  - 48  =  5 ID2 A. 

Capacity  in  pounds     =  -      -X62«5  =  49.i D2A . 

For  practical  purposes  it  is  accurate  enough  to  use  $oD2A 
for  the  last  expression,  the  error  being  less  than  2%,  and  on  the 
side  of  safety. 

Capacity  of  Cone. 

Capacity  in  cubic  feet  =  — -^  = 


112  TOWERS  AND    TANKS  FOR    WATER-WORKS. 


Capacity  in  gallons     =  —     —  Xfj.4&=i.g6D2Al. 


Capacity  in  pounds     =  -  -X  62.5  = 


Capacity  of  Segment  of  a  Sphere. 

Capacity  in  cubic  feet  =  %xR2s(2—  3  cos  w+cos3  &>), 

or     ±nA2*(3R2-A2). 
Capacity  in  gallons      =  7.84^23(2—  3  cos  aj-\-  cos3  co), 

or     7.84.422(3^2-^2). 

Capacity  in  pounds      =  65.5^23(2—  3  cos  cu+  cos3  a>), 
or      6. 


Capacity  of  Hemisphere.  —  The  hemisphere  may  be  considered 
a  special  case  of  the  segment  of  a  sphere  in  which  A2  =  R2  = 

—  ,  and  6^  =  90°;  then 

Capacity  in  cubic  feet  =  ---  =o.262jD3. 

Capacity  in  gallons       =  i.g6D3. 
Capacity  in  pounds      =i6.^6D3. 

Areas  of  Surfaces.  —  The  areas  of  the  surfaces  are  needed  for 
computing  the  weight  of  metal  in  the  shell.     They  are: 

Cylinder.  .  .  .  area  in  square  feet  =  nDA  . 
Cone  ......  area  in  square  feet  =%7rDA1  sec  6. 

AD2          \ 
Segment.  .  .  .area  in  square  feet  =TT(  ---  [-A22  ),  or  2nR2A^ 

Hemisphere,  area  in  square  feet  =  %nD2. 

Stresses  in  the  Cylinder.  —  The  stress  on  a  horizontal  joint  of 
a  vertical  cylinder,  or  on  the  section  made  by  a  horizontal  plane, 


THE   STRES:SES  IN  A    STEEL    WATER-TOWER.         113 

mm  (Fig.  19),  is  compression.  Its  amount  equals  the  weight 
of  the  portion  of  the  structure  above  the  plane  in  question.  Or- 
dinarily this  is  the  weight  of  the  tank  plates  and  roof.  In  cold 
climates  it  may  be  increased  by  ice  adhering  to  the  tank.  There 
is  no  appreciable  direct  stress  on  a  horizontal  joint  resulting 
from  hydrostatic  pressure.  The  compression  per  lineal  inch 

W 
of  circumference  of  the  joint  is  - — ,  in  which  W  is  the  weight 

in  pounds  supported  on  the  whole  circumference  and  r  is  the 
radius  in  inches. 

The  stress  on  a  vertical  joint  of  the  cylinder  is  produced  by  the 
hydrostatic  pressure  on  the  inside  of  the  cylinder.     This  pres- 


in  1 1  n  in 

FIG.  19. 


m 


FIG.  20. 


sure  is  normal  to  the  surface,  therefore  radial,  and  its  intensity 
in  pounds  per  square  inch  of  surface  is  ^  =  0.434^?.  Assume 
a  ring  one  inch  in  height  cut  from  the  cylinder  at  a  depth  of  H 
feet  from  the  top.  The  internal  pressure  will  then  be  p  pounds 
per  lineal  inch  of  the  ring  (Fig.  20). 

Pass  a  diametral  plane  mn  cutting  the  ring  at  m  and  n, 
and  consider  the  half  to  the  right  of  mn.  To  maintain  equilib- 
rium of  the  half-ring  the  forces  Tm  and  Tn  must  act  at  m  and  n 
respectively.  Then  Tm  and  Tn  equal  the  tension  in  the  shell 
at  m  and  n.  By  symmetry  Tm=Tn. 


114  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

By  mechanics*  it  can  be  shown  that  Tm=Tn  =  \lX  com- 
ponents of  the  radial  pressures  =  pr. 

Since  the  diametral  plane  can  be  in  any  position,  the  tension 
is  the  same  at  all  points  on  the  circumference  of  the  ring. 

Taking  n  as  a  centre  of  moments, 

Mn  =  2prXr-TmX2r=o, 

hence  there  is  no  bending  moment  in  the  shell. 
Consider  now  a  quarter-ring  ml. 

T,-Tm, 

TI  —2Y  components  of  p=ot 
Tm—IX  components  of  p  =  o\ 

therefore  there  is  no  horizontal  shear  at  m  or  at  /. 

Thus  it  is  shown  that  the  stress  on  a  vertical  joint  is  tension 
only,  and  the  amount  per  lineal  inch  of  joint  is  T=pr^o.^^Hr9 
where  T  is  the  tension  in  pounds  per  lineal  inch  of  the  joint. 
Note  that  if  p  acts  inward  instead  of  outward  we  have  compres- 
sion instead  of  tension. 

Stresses  in  the  Cone. — To  find  the  stress  on  a  circumferential 
joint  or  on  the  section  cut  by  a  horizontal  plane  (Fig.  21),  let 
ee  be  such  a  section.  The  load,  W,  on  the  cone  ee}  is  the  weight 
of  the  cylinder  of  water  whose  base  is  ee  and  whose  height  is 
the  distance  from  ee  to  the  top  of  the  tank,  plus  the  weight  of 
water  in  the  cone  ee},  plus  the  weight  of  steel  in  the  cone  eej. 
This  load  must  be  supported  by  the  forces  T  acting  along  the 
elements  of  the  cone  and  around  the  perimeter  of  ee.  Then 
IT  =  W  seed. 

The  forces  T  equal  the  tension  on  the  joint.  This  tension 
is  uniformly  distributed  on  the  perimeter  of  ee.  Hence  the 

*  For  proof  see   page         ;   also  "Stresses  in  Tank  Bottom,"  by  Prof.  A.  N. 
Talbot,  in  The  Techno  graph,  No.  16,  page  137. 


THE  STRESSES  IN  A    STEEL    WATER-TOWER.         115 

W  sec  0 
tension  per  lineal  inch  of  joint  is  T= 7 — ,  where  ftx  is  the 

radius  of  the  section  in  inches. 

The  value  of  T  varies  from  o  at  /  to  a  maximum  at  g.     It 
also  varies  from  o  when  #  =  o°  (cylinder)  to  infinity  when. 6  =  go0 


FIG.  22. 

(plane),  i.e.,  the  flatter  the  cone  the  greater  the  stress  on  the 
circumferential  seams. 

To  find  the  stress  on  a  radial  joint  pass  two  horizontal  planes 
through  the  cone  at  such  distances  apart  that  the  intercept  eh 
along  the  elements  of  the  cone  equals  one  inch  (Fig.  22).  Then 
the  surface  ehhe  cut  from  the  cone  is  a  tapered  ring.  This 
ring  is  subjected  to  a  normal  pressure  of  p  pounds  per  lineal 
inch.  For  p  substitute  its  components  if  and  p"  which  are 
horizontal  and  along  the  elements  of  the  cone  respectively. 


By  reasoning  similar  to  that  used  in  determining  the  stress  on 
a  vertical  joint  of  the  cylinder  it  may  be  shown  that  the  horizontal 
component  if  produces  tension  in  the  ring.  Let  T  be  the  tension 
per  lineal  inch  of  the  radial  joint,  then  T=pfbl  =  pbl  sec  6,  where 
bl  is  the  radius  of  the  ring  in  inches,  b^  sec  6  is  represented 
graphically  by  the  line  ab,  hence  T=pXab. 

The  value  of  T  varies  from  o  at  /  to  a  maximum  at  g. 


Il6  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

The  component  p"  together  with  the  similar  components 
acting  on  the  elements  between  h  and  /  produce  tension  on  the 
horizontal  joint  through  e,  the  amount  of  which  has  already  been 
determined. 

Stresses  in  the  Segment  of  a  Sphere.— The  stress  on  a  cir- 
cumferential joint  of  the  segment  of  a  sphere  is  determined  by 
analysis  similar  to  that  used  for  the  cone  (Fig.  23).  The  tension 
on  one  lineal  inch  of  the  joint  ee  is 

Wcsca/ 


in  which  W  is  the  weight  supported  by  the  segment  eje,  and  b2 
is  the  radius  of  the  section.  Let  r2  be  the  radius  of  the  sphere, 
then 

62  =  r2sin  a/, 
and 

W  esc2  to' 

27ZT2 

The  tension  per  lineal  inch  on  any  meridian,  or  radial,  joint 
of  a  sphere  subjected  to  an  internal  normal  pressure  of  p  pounds 

per  square  inch  is  T= — -.  From  this  it  is  inferred  that  the 
tension  per  lineal  inch  at  any  point  e  of  a  radial  joint  of  a  seg- 

lyy 

mental  bottom  is  T= — -,  p  being  the  normal  pressure  per  square 
inch  at  e* 

When  the  bottom  is  a  hemisphere  r2  =  r,  then  T= — . 

The  value  of  T  varies  with  the  pressure,  p,  and  hence  is  a 
maximum  at  the  bottom  of  the  segment. 

*  See  "Stresses  in  Tank  Bottoms,"  by  Professor  Arthur  N.  Talbot,  The  Tech- 
nograph,  No.  16,  page  138. 


THE   STRESSES  IN  A    STEEL    WATER-TOWER.         \\J 

Stresses  in  the  Joint  Between  the  Bottom  and  the  Cylinder. 

— The  vertical   load,  TF,  on  this  joint    equals  the  total  weight 
of  water  in  the  tank  plus  the  weight  of  the  tank  bottom,  and  is 


hS* 


V 


FIG.  23. 


FIG.  24. 


transmitted  thereto  by  the  plates  forming-  the  bottom.  The 
tension  per  lineal  inch  in  these  bottom  plates  at  this  joint  is  de- 
termined from  the  formula 


sec 


for  the  cone  (Fig.  21)  and 


Wcsca/ 


for  the  segment  of  the  sphere  (Fig.  23).     At  this  joint  b^  and 
equal  r,  and  the  above  formulas  become  respectively 


,and 


Wsecff 


TFcsc  a> 


This  tension  in  the  bottom  plates  will  be  treated  as  the  load 
on  the  joint. 


Il8  TOWERS  AND    TANKS   FOR    WATER-WORKS. 

When  the  tank  bottom  is  conical  (Fig.  24)  the  load  T  on  the 
joint  is  applied  along  the  elements  of  the  cone.  To  provide  for 
its  resistance  it  must  be  resolved  into  its  horizontal  and  vertical 
components  H  and  V. 

W  sec  0  W  tan  6 

H  =  T  sin  6  =  -    -  Xsm  6  =  -  , 

27ZT  27tr 


W  sec  6  W 

-        -Xcos0  =  —  . 


The  horizontal  component  is  a  uniform  radial  force  amount- 

TFtanfl 
ing  to  -  pounds  per  lineal  inch  of  perimeter  pulling  toward 

the  axis  of  the  cylinder.  This  produces  compression  in  the 
ring  of  material  constituting  the  joint.  Using  this  normal  pres- 
sure and  considering  the  ring  cut  by  a  vertical  plane,  it  will  be 
seen  that  the  total  compression  on  a  section  of  the  ring  is 

W  tan  6 
C=  -  Xr  =  o.i59TFtan  0. 

The  vertical  component  V  is  resisted  by  the  circular  girder. 
Its  analysis  will  be  considered  hereinafter. 

Considering  the  segmented  bottom  (Fig.  24)  in  a  similar  manner, 

W  CSC  CD  W  COt   0) 

H=T  cos  oj=—     —  -  X  cos  o)  =  —  -  ; 


_.          .          W  esc  a)      .  W 

V=Tsmco  = 


C  =0.159  W  cot  oj. 
When  aj  =  go°  the  bottom  is  a  hemisphere  and  H  and  C  become  o. 


THE   STRESSES  IN  A    STEEL    WATER-TOWER.         IIQ 

It  is  this  that  makes  the  hemisphere  the  most  desirable  form  of 
bottom. 

It  will  be  noted  that  the  value  of  V  is  independent  of  the 
shape  of  the  bottom. 

The  above  analysis  assumes  that  the  joint  is  theoretically 
perfect,  that  is,  that  the  lines  of  action  of  H,  V,  and  T  inter- 
sect in  a  common  point.  In  the  case  of  both  the  conical  and  the 
segmental  bottoms  the  plates  have  to  be  flanged  so  as  to  become 
tangent  to  the  cylinder.  Thus  the  element  of  the  cone  and  the 
element  of  the  cylinder  must  be  connected  by  a  curve,  likewise 
the  meridian  element  of  the  segment  and  the  element  of  the 
cylinder  (Fig.  25).  This  connecting  curve  may  be  part  of  a  sphere 


FIG.  25. 

or  part  of  an  ellipsoid  of  revolution.     In  the  former  case  r3  equals 
r,  and  in  the  latter  case  r3  is  less  (or  greater)  than  r. 

The  stresses  in  this  connecting  part  of  the  bottom  are  com- 
plex.    An  analysis  of  them  is  given  by  Professor  Talbot,*  from 

which  it  seems  that  when  the  ratio  of  -  =  2,  H  =  o  and  there  is 

rs 

no   resulting  tension  or  compression  on  the    joint-ring;    when 
-<2   there  is  tension;    and  when  ->2   there  is  compression. 


*  See  "Stresses  in  Tank  Bottoms,"  by  Professor  Arthur  N.  Talbot,  The  Tech- 
nograph,  No.  16,  page  139. 


120 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 


As  it  is  easier  in  construction  to  provide  for  the  tension,  it  seems 
advisable  to  make  the  value  of  —  =  or<2.     When   the  bottom 

rz 

is  a  hemisphere  —  =i,  that  is,  r  =  ry 
rz 

If  rz  is  made  very  small  in  comparison  with  r,  there  are  un- 
doubtedly bending  stresses  in  the  plate.  The  amount  of  these 
stresses  cannot  be  determined  readily,  consequently  they  should 
be  avoided. 

It  will  generally  be  most  satisfactory  to  use  the  hemispherical 
bottom,  as  all  stresses  will  then  be  determinate.  Such  bottoms 
can  now  be  manufactured  without  undue  expense. 

Stresses  in  the  Circular  Girder.— The  circular  girder  sustains 
the  vertical  component  just  determined  plus  the  weight  of  the 
steel  cylinder,  the  tank  roof,  and  its  own  weight.  That  is,  it 


FIG.  26. 


supports  the  whole  weight  of  the  tank,  the  contents  of  the  tank, 
and  itself.     This  load  is  uniformly  distributed  along  the  girder. 


THE   STRESSES   IN  A    STEEL    WATER-TOWER.         121 

The  girder  rests  on  the  tops  of  the  tower  posts,  and  transmits 
the  load  to  them.  There  may  be  four  or  more  posts  or  points 
of  support. 

Consider  first  a  girder  with  four  points  of  support.*  Let  W 
be  the  total  load,  and  let  A ,  B,  C,  and  D  be  the  points  of  support 
of  the  circular  girder  (Fig.  26).  By  symmetry  the  reactions  RAJ 

W 

RB,  Rc,  and  RD  are  equal  to  each  other,  hence  each  is  R  =  — . 

4 

Assume  the  axes  of  reference  X,  Y,  and  Z  passing  through  O, 
the  axis  of  Z  being  vertical.  Consider  the  left  half  of  the  girder 
cut  away  by  a  plane  just  to  the  left  of  the  points  of  support  A 
and  C.  The  forces  required  to  maintain  the  equilibrium  of 
the  right  half  equal  the  stresses  in  the  girder  at  A  and  C.  The 
possible  forces  at  A  are 

a  horizontal  force  parallel  to  X=+SX', 

a  horizontal  force  parallel  to  Y=+Sy] 

a  vertical  force  parallel  to  Z=  +  SZ] 

a  couple  perpendicular  to  X,  whose  moment  —+MX'9 

a   couple  perpendicular  to    F,   whose  moment  =+My; 

a  couple  perpendicular  to  Z,  whose  moment 

and  at  C  the  possible  forces  are 

-}-Sx,      —Sy,      and     -\-Sz] 
—  Mx,     +My,     and     —  Mz. 


The  external  forces  acting  on  the  portion  of  the  girder  considered 

W 

are  — ,  RA,  R£,  and  Rc.    These  external  forces  have  no  com- 
ponents parallel  to  X,  hence 

Likewise  Sy  =  o. 

*  Adapted  from  "The  Bending  Moment  in  a  Circular  Girder,"  by  G.  P.  Stark- 
weather, Engineering  News,  Nov.  15,  1900. 


122  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

From  the  summation  of  the  Z  components, 
— 

Z        2 

W 


w 


which  is  the  vertical  shear  in  the  girder  at  the  sections  to  the 
left  of  A  and  C. 

Let  G  be  the  centre  of  gravity  of  the  load  on  the  half-girder. 

The  distance  OG  is  —  ,  in  which  r  is  the  radius  of  the  girder. 

W 

Por  determining  moments  the  load  on  the  half-girder,  —  ,  will 

be  considered  as  acting  at  G. 

MX  and  Mg  are  indeterminate  from  the  conditions  given, 
but  from  other  considerations  it  can  be  shown  that 


and  A 

My  is  determinate. 

W    2 

a/  =Er/i_L\ 

y~    2    \4        7T/ 

=  0.0341  $Wr, 
which  is  the  bending  moment  in  the  girder  at  A  and  at  C. 


THE   STRESSES  IN  A    STEEL     WATER-TOWER. 


123 


To  determine  the  stresses  at  any  point  between  supports, 
consider  the  arc  AP,  A  being  a  point  of  support  and  P  an  inter- 
mediate point  at  which  the  stresses  are  required.  Assume  the 
axes  of  X',  Y',  Z'  through  P.  Let  a  be  the  angle  AOP  expressed 
in  circular  measure,  then  the  load  on  AP  is 


Wa 

271 


The  centre  of  gravity  of  the  load  is  at  G. 
The  geometric  relations  of  the  figure 
are  (Fig.  27) 


2  rsm  — 


VAX    ,. 


FIG.  27. 


.    a        a 

2r  sin  —  cos  — 

— =  2     rsrna 


a 


a 


rsma     r          . 

— (a—  sina); 
' 


a         a 

a 


2r  sn 
QG=  —  —  -  -  5(1-  cos  a)  ; 


=  r  sn  a; 
=  ri  —  cos  a 


W 

The  known  forces  acting  on  AP  are  the  vertical  shear  Sz=  — 

o 

on  the  left  of  ^4,  the  reaction  RA,  the  couple  at  A  whose  moment 

Wrfi      i' 
=  —  '  --- 


is      u  = 


Wa 
,  and  the  load . 

2    \4        n  )  27T 


124  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

The  unknown  forces  are  those  required  at  P  to  maintain 
equilibrium  and  equal  the  stresses  in  the  girder  at  P.  The  pos- 
sible forces  at  P  are 

a  horizontal  force  parallel  to  Xf=-}-Sfx\ 

a  horizontal  force  parallel  to   F'=+S£; 

a  vertical  force  parallel  to  Zf  =  +  S'z ; 

a  couple  perpendicular  to  X'  whose  moment  =M^; 

a  couple  perpendicular  to  F'  whose  moment  =  M'y\ 

a  couple  perpendicular  to  Z'  whose  moment  =  Mg. 

By  summation  of  components, 
Si-o; 


= — = — (—_  —  ). 

4         8          27T          2  \4        JC/ 

?J  is  a  maximum  when  a  =  o;  then 


when   «  =  -, 

4  «-o; 


that  is,  the  point  of  zero  shear  is  midway  between  supports. 

Since  the  only  horizontal  forces  acting  are  couples  in  verti- 
cal planes, 


, 

THE   STRESSES  IN  A    STEEL    WATER-TOWER.         12$ 

The  moment  at  P  about  the  axis  of  Xf  is  a  torsional  moment, 


M'x  =  My  sin  a  ---  QP+—SP 

27T  O 

Wr/i      i  \  .          WV 


TFr,  Wra 

--(i  +  sm  a—  cos  a)  —  --  ^. 


27T 

MX  =  O  when  a  =  o  and  when   a  =—,  i.e.,  there  is  no  torsional 

4 

moment  at  the  point  of  support  nor  midway  between  supports. 
To  determine  the  place  of  maximum  value  of  M'xt 

dMl     Wr  Wr 

—; — =  — ^cos  a  +  sin  a) =  o. 

CLOL  O  27T 

4 
cos  a+sm  a  =  -  =  1.2732, 

a  =  19°  1 2' or  70°  48', 
and  the  maximum  values  are 

M'x=  —  o.oo$sWr  when  a  =  19°  12' =  0.3351  radians, 
and     Mi  =  +  0.005  3 Wr  when  a  =  70°  48'  =  1.2356  radians. 

The  moment  at  P  about  the  axis  of  Yf  is  the  bending  moment 
in  the  girder  at  P.     It  is 

Wa W 

My  =  My  cos  a QG+ -$-AS 


27T 

W 


Wr/i      i\  War, 

'•  —  (-—  -  )  cos  a  ---  (i  —  cos  a 
2  \4  '  *y  zx  cr 


—rsma 
8 


126  TOWERS  AND    TANKS   FOR    WATER-WORKS. 


Wr     .  x     Wr 

—  -5—  (sin  a  +  cos  a)  —  — . 

O  27T 


When  a  =  o, 

MV~     2     V4        * 


Wr  /i      i  \ 

~)=-  °'°34i  $Wr, 


which  is  the  bending  moment  in  the  girder  over  the  point  of 
support. 


When  a  =  —  , 
4 


My  =  ——l  1.4142—  -  1 


which  is  the  bending  moment  in  the  girder  midway  between 
supports. 

Between  the  values  of  a  =  o  and  a  =  —  there  must  be  a  value 

4 

of  a  that  will  make 

Wr  t  Wr 

My  =  —~-(sm  a+cos  a)—  -  =  o, 

from  which 

sin  a  +  cos  a  =  1.2732, 
and  a  =  19°  12'  or  70°  48'. 

A  comparison  of  the  values  obtained  for  Mfx  and  My  shows 
the  following  important  results 

1.  The   points   of  maximum   torsion   moment   are   points  of 
zero  bending  moment. 

2.  The  points  of  maximum  bending  moment  are  points  of 
zero  torsion  moment. 

Considering  now  girders  having  a  number  of  points  of  sup- 
port other  than  four,  we  can  make  analyses  similar  to  the  fore- 
going. Their  results  for  several  cases,  including  the  results 


7 'HE   STRESSES  IN  A    STEEL    WATER-TOWER.         I2/ 


just  obtained  for  the  four  points  of  support,  are  summarized  in 
the  following  table: 

STRESSES  IN  THE  CIRCULAR  GIRDER. 


Angular 

No.  of 
Points 
of 
Support. 

Reaction 
at  Point 
of 
Support  . 

Max. 
Shear. 

Bending  Mo- 
ment over 
Point 
of 
Support. 

Bending  Mo- 
ment midway 
between 
Supports. 

Distance 
Point  of 
Support 
to  Point 
of 
Maximum 

Maximum 
Torsional 
Moment. 

Torsion. 

Pounds. 

Pounds. 

Inch-pounds. 

Inch-pounds. 

Inch-pounds. 

W 

W 

—  0.0341  5  Wr 

-f-o.  01762  Wr 

10°  12' 

o  005  3  Wr 

4 

8 

W 

W 

6 

—  o.  01482  Wr 

-\~  0.0075  *  Wr 

12°  44' 

o.ooi$iWr 

6 

12 

W 

W 

8.  . 

—  o.  00827  Wr 

-|-  0.0041  6  WV 

9°  3  3' 

o.  00063  Wr 

8 

16 

12  

W 

W 

—  o.ooT.6^Wr 

-{-o.ooigoWr 

6°2l' 

o.oooi8"$Wy 

12 

24 

In  the  above  table  W  is  the  total  weight  supported  by  the 
girder  in  pounds,  and  r  is  the  radius  of  the  girder  in  inches. 

Stresses  in  the  Posts. — It  was  shown  in  the  consideration  of 
the  circular  girder  that  the  vertical  load  on  the  top  of  a  post  is 
the  total  weight  of  the  circular  girder,  the  tank  and  its  contents- 
divided  by  the  number  of  posts.  In  addition  to  this  load  the 
posts  of  each  story  must  carry  the  weight  of  posts,  struts,  and 
ateral  rods  of  the  stories  above  it.  Thus 
the  vertical,  load  on  any  one  section  or  story 
of  the  post  is  readily  determined.  Let  the 
vertical  load  on  the  section  under  considera- 
tion be  W.  If  the  post  is  vertical,  the  com- 
pression in  it  equals  W.  If  the  post  is 
inclined,  the  compression  becomes 

C=TFsec  0,     (Fig.  28,) 

</>  being  the  angle  of  inclination  of  the  post 
from  the  vertical.  The  vertical  reaction  at 
the  base  of  the  post  equals  W.  To  maintain  equilibrium  there 


w 


FIG.  28. 


128 


TOWERS  AND    TANKS   FOR    WATER-WORKS. 


must  be  a  horizontal  reaction  H  at  the  top  and  at  the  bottom 
of  the  post,  in  the  same  vertical  plane  as  the  post,  i.e.,  in  a 
diametral  plane. 


If  the  inclination  is  expressed  in   rectangular  co-ordinates, 


and 


C=W 


When  there  is  a  change  in  the  inclination  of  the  post  there 
must  be  a  horizontal  reaction  in  a  diametral  plane  at  the  point 
of  change.  Let  Hf  be  this  reaction.  Then 


=  H"-H 


-  W  tan 


or 


Stresses  Resulting  from  the  Horizontal  Thrust  at  the  Top 
of  the  Posts. — At  the  top  of  each  post  there  is  a  radial  inward 


FIG.  29. 

thrust  whose  value  has  been  determined  from  the  vertical  load 
and  inclination  of  the  post.     Let  H  be  the  amount  of  this  thrust. 


THE   STRESSES  IN  A    STEEL    WATER-TOWER. 

When  struts  between  diagonally  opposite  posts  are  used 
to  resist  this  thrust  the  compression  in  each  strut  equals  H. 
(Fig.  29.) 

If  struts  are  not  used,  the  radial  forces  may  be  resisted  by 
the  bottom  flange  of  the  circular  girder.  Since  the  width  of 
the  girder  flange  is  small  compared  with  the  radius  of  the  girder, 
the  solution  of  the  stresses  in  a  circular  hoop  may  be  applied- 

When  a  pair  of  radial  forces  H  act  on  a  hoop,  as  at  A  and  C 
(Fig.  30),  the  stresses  at  any  point  /  resulting  therefrom  are:* 

Bending  moment,  M'  =  Hri-       ~~j- 

TT 

Shear,  S'   =  —  cos  a'. 

TT 

Compression,          Cr  = — sin  a'. 


A  second  pair  of  forces  H  acting  at  B  and  D  produce  stresses 
at  I: 

sin  a." 


C"  =—  sin  a". 

2 

Then  the  stresses  at  /  resulting  from  both  pairs  of  forces  are 
the  algebraic  sums  of  the  partial  stresses.  The  general  equa- 
tions for  these  stresses  when  the  forces  are  in  equal  pairs  are 

*  Transactions  Association  of  Civil  Engineers,  Cornell  University,  1896. 


130 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 


•>,      Hrr  -        ,        •        „  •  nHr 

M= [sin  «  +  sin  a"+ . . .  sin  a"] , 


TT 

S  = — [cos  a'+ cos  a"  + . . .  cos  aM], 


TT 

C  = — [sin  a'+ sin  a"   + . . .  sin  att], 


n  being  the  number  of  pairs.     2n  equals  the  number  of  forces 
acting,  i.e.,  the  number  of  posts  supporting  the  circular  girder. 
From   the   above   general   equations   the   following   table   of 
stresses  results: 


STRESSES  IN  RING  AT  TOP  OF  POSTS. 


Number 
of 
Posts. 

Bending  Moment. 

Shear. 

Compression. 

Under  Load. 

Midway 
between 
Loads. 

Under 
Load. 

Midway 
between 
Loads. 

Under 
Load. 

Midway 
between 
Loads. 

Inch-pounds. 

Inch-pounds. 

Pounds. 

Pounds. 

Pounds 

Pounds. 

4  

—  o.itfHr 
-o.oSgHr 
—  0.067  Hr 
—  o  OAdHr 

-\-o.ojosHr 
+  0.045  Hr 
+  0.033  Hr 
+  0.022  Hr 

O.^oH 
0.50.2? 
o.$oH 
o.$oH 

0.00 
0.00 

o.oo 
o.oo 

0-50.H" 
0.87^ 

I.2IH 

i.SjH 

o.yoyH 
i.  oo  H 
1.31  H 
1.93  H 

6  

8 

12.  . 

In  the  above  table  H  is  the  horizontal  thrust  in  pounds  at 
the  top  of  each  post,  and  r  is  the  radius  of  the  ring  in  inches. 

This  radius  is  approximately  equal  to  the  radius  of  the  tank 
cylinder. 

In  many  cases  the  ring  formed  by  the  bottom  flange  of  the 
circular  girder  is  not  sufficient  to  resist  the  stresses  resulting 
from  the  thrust  at  the  top  of  the  posts,  without  using  a  large 
amount  of  metal  in  the  ring.  This  will  be  the  case  in  large  struc- 
tures when  the  posts  have  considerable  inclination.  In  such  a 


THE    STRESSES  IN  A    STEEL    WATER-TOWER.         13! 

case  a  continuous  curved  girder  in  the  horizontal  plane  may  be 
used  (Fig.  31). 

The  stresses  in  this  horizontal  girder  can  be  determined  by 
treating  it  as  an  arch  without  hinges.  Assume  the  girder  to 
be  cut  in  two  equal  parts  by  the  plane  mm.  Then  the  half-girder 


ABD  will  form  a  semicircular  arch,    sustaining  a  load  of  H 

TT 

pounds  at  the  crown  and  a  thrust  of  —  pounds  at  each  abut- 
ment. At  each  abutment  there  is  also  a  couple  whose  moment 
must  be  determined  in  order  to  find  the  stresses  in  the  girder. 
The  bending  moment  at  the  abutment  and  the  resulting  bend- 
ing moments  at  the  other  points  in  the  arch  may  be  determined 
by  the  methods  usually  employed  in  the  analysis  of  the  elastic 
arch.  Graphical  analyses  of  the  stresses  in  horizontal  curved 
girders  having  four,  six,  eight,  and  twelve  loaded  points,  or  points 
of  support,  give  coefficients  varying  not  more  than  three  per  cent, 
from  those  given  in  the  table  of  Stresses  in  Ring  at  Top  of 
Posts  (page  130).  Strict  mathematical  analysis  would  probably 
give  identical  results.  In  any  case,  the  variation  is  so  small 


132  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

that  the  table  just  referred  to  can  be  used  for  determining  the 
stresses  in  a  horizontal  curved  girder. 

In  using  this  table  for  determining  the  stresses  in  a  horizontal 
curved  girder,  the  value  of  H  to  be  used  is  the  horizontal  thrust 
in  pounds  at  the  top  of  each  post,  and  the  value  of  r  to  be  used 
is  r4,  as  shown  in  Fig.  31,  i.e.,  the  radius  of  the  neutral  axis 
of  the  girder  in  inches.  The  value  of  r4  is  approximately  r, 
the  radius  of  the  tank  in  inches,  plus  %d,  d  being  the  width  of 
the  girder  in  inches.  This  approximate  value  is  sufficiently 
accurate  for  determining  stresses. 

The  flange  stress  in  the  girder  resulting  from  the  bending 
moment  can  be  determined  by  dividing  the  bending  momriit. 
by  the  depth,  d,  centre  to  centre  of  flanges  in  inches.  To  this 
flange  stress  must  be  added  algebraically  the  compression  at 
the  point  under  consideration.  It  is  proper  to  consider  that 
the  compression  is  resisted  by  the  flanges  of  the  girder  and  divided 
equally  between  them.  As  in  ordinary  plate-girder  design,  the 
shear  may  be  considered  to  be  resisted  by  the  web  plate. 

If  a  lattice  girder  is  used  instead  of  a  plate  girder,  the  bending 
moment  at  the  abutments  of  the  arch  may  be  replaced  by  a  couple 
whose  lever-arm  is  the  depth  of  the  girder  centre  to  centre  of 
flanges.  From  these  reactions  and  the  loads  the  stresses  in 
the  members  of  the  lattice  girder  may  be  determined  by  graphical 
methods. 

Horizontal  Stresses  at  Plane  of  Change  of  Inclination  of 
Posts. — The  amount  of  the  horizontal  thrust  at  each  post  at  the 
point  of  cnange  of  inclination  has  been  determined.  Let  H' 
represent  this  thrust  (Fig.  32).  Then  if  the  thrust  is  resisted 
by  struts  between  diagonally  opposite  posts,  as  AD,  the  com- 
pression in  each  strut  equals  H'.  If  the  thrust  is  resisted  by 
struts  between  adjacent  posts,  as  AB,  the  compression  in  each 
strut  equals 

H' 

—  sec/?. 


THE   STRESSES  IN  A    STEEL    WATER-TOWER. 


133 


Horizontal  Stresses    at    the  Base  of   the  Tower. — The 

amount  of  the  horizontal   thrust   at   the   foot  of  each  post  has 
been  determined.     This  thrust   may  be  resisted  by  direct  shear 


FIG.  33. 


on  the  anchor-bolts,  or  by  the  friction  of  the  shoe  on  tne 
masonry,  or  by  both.  When  thus  resisted  the  thrust  produces 
an  overturning  moment  on  the  foundation  (Fig.  33). 

Or  ties  may  be  used  between  adjacent  posts.     Then  the  stress 

TT 

in  each  tie  is  —  sec  /?,  and  there  is  no  overturning  moment  on 
the  foundation. 


WIND    STRESSES. 

The  intensity  of  wind  pressure  depends  on  the  area  of  the 
surface  exposed  and  the  velocity  of  the  wind.  The  relation  be- 
tween these  two  quantities  is  not  known,  but  in  general  it  can 
be  said  that  the  larger  the  area  the  less  the  intensity,  and  the 
greater  the  velocity  the  greater  the  intensity.  The  action  of  a 
wind  current  is  probably  analogous  to  the  action  of  a  stream 
of  water.  Obstructions  produce  cross-currents  and  eddies, 
making  the  pressure  on  a  given  unit  area  of  the  exposed  surface 
variable.  The  shape  of  the  exposed  surface  doubtless  in- 
fluences the  intensity.  Water-towers  are  usually  placed  in 
exposed  positions.  Their  importance  makes  it  advisable  that 
they  be  designed  to  withstand  the  greatest  wind  pressure  that  is 


134  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

likely  to  occur.  Since  wind  stresses  do  not  control  the  design  of 
the  heavier  parts  of  the  structure,  there  is  but  little  excess  ma- 
terial used  if  the  assumed  wind  pressure  is  greater  than  the  actual 
wind  pressure.  The  writer  considers  it  good  practice  to  design 
water-towers  to  withstand  a  wind  pressure  of  30  pounds  per 
square  foot  of  projected  area  of  the  tank  and  the  members  of  the 
tower. 

Stresses  in  the  Cylinder.—  Under  the  assumption  made 
above,  the  forces  acting  on  the  cylinder  will  be  as  shown  in  the 
diagram  (Fig.  34).  The  cylinder  may  be  treated  as  a  cantilever 
beam.  Then  the  bending  moment  at  the  fixed  end  in  inch- 
pounds  is 


The  extreme  fibre  stress  resulting  is  determined  from  the  formula 

Mr 

~~ 


in  which  5  is  the  extreme  fibre  stress  per  square  inch,  M  is  the 
bending  moment  just  determined,  r  is  the  distance  in  inches  of 
the  extreme  fibre  from  the  centre,  which  in  this  case  is  the  radius 
of  the  cylinder,  and  /  is  the  moment  of  inertia.  The  moment 
of  inertia  of  a  thin  cylinder  about  a  diameter  is 


t  being  the  thickness  of  the  shell.     Then 

iSoA2DXr  A2 


In  water-towers  of  usual  dimensions  this  stress  is  small,  but  in 
stand-pipes  and  chimneys  it  may  become  large.  The  local  bend- 
ing stresses  are  indeterminate. 


THE  STRESSES.   IN  A   STEEL    WATER-TOWER. 


135 


The  wind  stresses  in  the  tank  bottom  and  in  the  circular 
girder  cannot  be  definitely  determined.  They  are  probably 
small  in  comparison  with  the  gravity  stresses. 

Stresses  in  the  Tower. — The  wind  loads  acting  on  the  tower 
are  the  loads  transmitted  to  it  by  the  tank  and  the  direct  wind 
pressure  on  the  members  of  the  tower.  The  former  are  applied 
at  the  tops  of  the  posts,  and  the  latter  will  be  considered  as  con- 
centrated at  the  panel  points. 

Consider  the  tank  a  rigid  body,  then  the  reactions  at  the 
top  of  the  posts  due  to  the  wind  pressure  on  the  tank  will  be  a 


FIG.  34. 

set  of  horizontal  forces  and  a  set  of  vertical  forces.  Let  P  be 
the  total  wind  pressure  on  the  tank,  including  the  roof. 

This  may  be  considered  as  acting  at  the  center  of  gravity  of 
the  projected  area.  (The  center  of  pressure  on  the  conical  bot- 
tom is  at  J  the  depth,  and  on  the  hemispherical  bottom  at  a  depth 

of  — .     The  pagoda  roof  may  be  reduced  to  an  approximately 

equivalent  cone  for  the  purpose  of  this  computation.)  Let  G 
be  the  distance  in  feet  from  the  tops  of  the  posts  to  the  centre  of 
gravity,  then  the  overturning  moment  in  foot-pounds  is 

M  =  PG. 

This  overturning  moment  must  be  resisted  by  the  connections  of 
the  tank  to  the  posts. 


136  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

The  distribution  of  the  vertical  forces  among  the  posts  is 
uncertain.  To  determine  it,  the  position  of  the  axis  about 
which  the  tank  tends  to  rotate  must  be  known.  This  depends 
on  the  rigidity  of  the  connections,  which  cannot  be  determined 
readily.  When  the  connections  give  the  same  resistance  to  ten- 
sion as  to  compression  the  axis  of  rotation  passes  through  the 
centre  of  the  polygon.  This  condition  obtains  when  the  posts 
are  riveted  directly  to  the  tank  cylinder.  When  the  resistance 
to  tension  is  very  small  compared  to  the  resistance  to  compression 
the  axis  of  rotation  is  near  the  extreme  leeward  post  (or  posts), 
This  condition  obtains  when  the  circular  girder  rests  on  top  of 
the  posts  and  is  bolted  thereto.  The  former  condition  gives 
a  maximum  tension  on  the  windward  side,  and  the  latter  a  max- 
mum  compression  on  the  leeward  side.  As  the  connections 
of  the  tank  to  the  post  should  be  rigid,  approximating  the  former 
condition,  that  case  only  will  be  considered. 

Assume  the  direction  of  the  wind  normal  to  the  side  EF  and 
the  axis  of  rotation  mm  (Fig.  35).  Since  the  stress  in  each  post 
is  proportional  to  its  distance  from  the  axis  of  rotation  mm,  the 
tension  VE=  VF=  —  VB=  —  Vc,  and  there  is  no  stress  at  A  and  ZX 
Taking  moments  about  mm,  the  moment  equation  is 

M  =   VX 


M  M 

--o.: 


in  which  M  is  the  overturning  moment  previously  determined, 
Next    assume  the  wind  in  the  direction  of  a  diagonal  EB 
and  the  axis  of  rotation  m'-m'  .      Then 


M-  (VA  +  Vc+  VD+  VF)o.SR+  (VB+ 


THE   STRESSES  IN  A    STEEL    WATER-TOWER. 
M  M 

V*  =  ^R  =  °'MR> 

M 


Thus  it  appears  that  the  maximum  vertical  load  due  to  wind 
pressure,  at  the  top  of  any  post,  results  when  the  wind  is  assumed 
in  the  direction  of  the  diagonal  passing  through  that  post. 

The  stress  in  each  post  resulting  from  a  given  direction  of 
the  wind  can  be  determined  readily  from  the  above  relations. 
The  method  of  analysis  is  applicable  to  a  tower  having  any  number 
of  posts. 

The  vertical  load  (either  tension  or  compression)  at  the  top 
of  a  post  being  determined,  the  stress  in  the  post  is  the  product  of 
the  vertical  load  and  the  secant  of  the  angle  of  inclination  as 
shown  under  gravity  stresses,  and,  as  in  the  case  of  gravity  stresses, 
there  is  a  horizontal  component  at  the  top  of  the  post.  As  these 
horizontal  components  at  the  tops  of  the  several  posts  are  not 
in  equilibrium,  they  must  be  transmitted  through  the  tower  to 
the  foundations. 

Considering  the  case  in  the  adjoining  figure  (Fig.  36),  these 
horizontal  components  are  about  as  represented  by  the  arrows 
marked  c,  the  dotted  arrow,  P,  indicating  the  direction  of  the 
wind.  The  value  of  each  must  be  determined  from  the  vertical. 
load  on  its  post  resulting  from  the  assumed  direction  of  the  wind. 
The  horizontal  components  .  will  be  combined  with  the  direct 
horizontal  shears  at  the  tops  of  the  posts  and  the  resulting  stresses 
in  the  tower  determined. 

The  set  of  horizontal  forces  previously  referred  to  consLts 
of  the  direct  shears  at  the  tops  of  the  posts.  It  will  be  assumed 
that  the  tank,  circular  girder,  and  horizontal  curved  girder  are 
capable  of  distributing  the  shear  equally  among  the  posts,  and 
that  the  segments  of  the  girders  from  post  to  post  are  capable 
of  acting  as  struts  of  the  tower  bracing.  Then  the  shear  at  each 


138 


TOWERS  AND    TANKS  fOR    WATER-WORR'S. 


post  is  — ,  acting  in  a  line  parallel  to  the  direction  of  the  wind. 
These  shears  are  represented  by  the  arrows  marked  s. 


FIG.  36. 

These  horizontal  loads,  c  and  s,  are  transmitted  to  the  foun- 
dations by  the  tower  frame.  To  determine  the  stresses  resulting, 
the  loads  must  be  resolved  into  their  components  lying  in  the 
planes  of  the  sides  of  the  tower.  These  components  are  shown 
by  the  dotted  arrows  (Fig.  36).  In  like  manner  the  panel  loads 


f 
THE  STRESSES  IN  A    STEEL    WATER-TOWER.         139 

at  the  successive  panel  points  are  resolved  into  the  planes  of  the 
sides  of  the  tower. 

Considering  the  side  of  the  tower  FAA'F1 ',  the  loads  acting 
thereon  are  as  indicated  (Fig.  37).  The  framing  forms  a  canti- 
lever truss  anchored  at  F'  and  A1 '.  The 

P1  A 

reactions  resulting  from  the  loads  on  this 
cantilever  can  be  computed  readily  from  the 
dimensions  of  the  structure  by  the  method  of 
moments  and  shears  (2  Moments  =  o,  I  Hori- 
zontal Comp.  =  o,  and  2  Vert.  Comp.  =  o). 
Having  determined  the  loads  and  reactions, 
the  stresses  in  the  truss  members  can  be  * 
solved  by  graphical  analysis.  Each  post  is 
common  to  two  adjacent  trusses  of  the  tower, 
and  its  total  stress  is  the  algebraic  sum  of  its  stresses  resulting 
from  its  membership  in  the  two  trusses. 

An  inspection  of  the  components  of  the  shear  at  the  top  of 
the  tower  (Fig.  36)  will  show  in  which  sides  of  the  tower  the 
maximum  stresses  occur  for  the  assumed  direction  of  the  wind, 
but  the  concurrent  stresses  in  the  adjacent  sides  or  trusses  must 
be  solved  in  order  to  determine  the  total  stresses  in  posts. 

If  the  inclination  of  the  sides  of  the  tower  changes  at  each 
story,  each  story  must  be  analyzed  separately.  The  anti-reac- 
tions at  the  base  of  one  story  become  the  loads  at  the  top  of  the 
next  lower  story. 

Loads  on  the  Foundations. — The  reactions  U  and  Ul  at 
Ff  and  A'  in  the  above  figure  (Fig.  37)  lie  in  the  plane  of  the 
side  of  the  tower  (i.e.,  the  plane  of  the  truss  under  consideration). 
This  plane  being  inclined  p°,  the  loads  on  the  foundation  resulting 
are  a  vertical  component, 

U  cos  p°,     or     t/j  cos  p°, 
and  a  horizontal  component, 

U  sin  p°,     or     Ul  sin  p°. 


140 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 


(Do  not  confuse  (£>,  the  inclination  of  the  posts,  and  p,  the  inclina- 
tions of  the  sides.) 

Each  foundation  is  common  to  two  trusses,  and  the  loads 
from  the  two  must  be  combined  algebraically.  And  in  addition 
to  these  there  is  the  direct  load  resulting  from  the  vertical  load 
at  the  top  of  the  post. 

The  total  vertical  load  due  to  wind  pressure  on  any  founda- 
tion, as  at  A,  is  the  sum  of  the  vertical  component  of  the  direct 

stress  in  the  post,  the  vertical  com- 
ponent of  the  reaction  U  of  the 
truss  AB,  and  the  vertical  compo- 
nent of  the  reaction  U^  of  the  truss 
AF,  due  attention  being  given  to 
the  signs. 

The  horizontal  load  due  to  wind 
pressure  (Fig.  38)  on  any  founda- 
tion, as  at  A ,  is  the  resultant  of  the 
horizontal  component  (radial)  of  the 
direct  stress  in  the  post  (a),  the 
horizontal  shear  from  the  truss  AB 
(b),  the  horizontal  shear  from  the 
truss  AF  (c),  the  horizontal  com- 
ponent of  the  reaction  U  of  the  truss  AB  (d),  and  the  hori- 
zontal component  of  the  reaction  Ul  of  the  truss  AF  (e).  If 
the  bottoms  of  the  posts  are  connected  by  struts  (ties),  the 
resultant  horizontal  load  on  each  foundation  equals  5  (Fig.  36), 
and  its  line  of  action  is  parallel  to  the  direction  of  the  wind. 


FIG.  38. 


CONCLUSION. 

The  possible  conditions  of  loading  for  a  water-tower  are: 

1.  Weight  of  structure. 

2.  Weight  of  structure  and  weight  of  water. 

3.  Weight  of  structure  and  wind  pressure. 


THE   STRESSES  IN  A    STEEL    WATER-TOWER.         14* 

4.  Weight  of  structure,  weight  of  water,  and  wind  pressure. 

Each  part  of  the  structure  must  be  designed  to  resist  the 
maximum  stress  that  can  result  from  any  combination  of  the 
above.  Generally  loading  No.  2  governs  the  design  of  the 
tank,  circular  girder  and  horizontal  curved  girder;  No.  3,  the 
anchorage,  the  tension  connections  of  tank  to  posts,  and  the 
bracing  of  the  tower;  and  No.  4,  the  posts  and  foundations. 

The  assumptions  made  in  the  analysis  for  wind  stresses  are 
believed  to  be  reasonable  and  on  the  side  of  safety.  When  there 
are  several  alternative  assumptions  that  one  should  be  used 
which  gives  maximum  results  for  the  member  under  considera- 
tion. The  wind  stresses  in  the  tank  shell  and  the  circular  girder 
are  indefinite,  but  it  is  believed  that  they  are  small  compared 
with  the  gravity  stresses  in  these  members,  and  can  be  neglected. 

In  some  cases  the  stresses  in  certain  members  are  so  small 
that  they  need  not  be  considered  in  designing.  However,  it  is 
not  safe  to  neglect  them  in  the  general  discussion,  since  in  struc- 
tures of  unusual  proportions  they  might  be  important. 


CHAPTER  VII. 
RIVETING. 

IN  structural  metal-work,  the  usual  method  of  uniting 
"  plates  "  or  of  connecting  t(  shapes  "  is  by  riveting. 

The  riveted  joint  is  technically  termed  a  "  lap-joint  "  when 
one  plate  overlaps  the  other.  It  is  a  "  butt-joint"  when  the 
two  plates  are  brought  together,  their  edges  in  contact,  and 
the  plates  fastened  by  the  use  of  a  cover-strip  or  "  welt,'* 
which  overlaps  both  plates ;  when  two  such  cover-strips  are 
used,  the  one  on  the  outside  and  the  other  on  the  inside  of 
the  two  plates  in  contact,  the  joint  is  termed  a  "  double-welt 
butt-joint." 

Such  joints  are  further  distinguished  as  being  "single- 
riveted"  when  a  single  row  of  rivets  is  used  as  fasteners  for 
the  two  plates.  It  is  a  "double-riveted  joint"  when  two 
rows  of  rivets  are  used;  so,  also,  "triple-riveted"  and 
"quadruple-riveted"  when  three  and  four  rows  respectively 
are  used  as  fasteners;  thus,  a  "triple-riveted,  double- welt 
butt-joint "  is  one  where  three  rows  of  rivets  are  used  in 
making  a  joint  between  two  plates,  covered  inside  and  out 
with  covering-strips  or  "welts." 

In  the  correspondence  columns  of  the  Engineering  News, 
Mr.  Freeman  C.  Coffin,  M.  Am.  Soc.  C.  E.,  in  discussing 
"Specifications  for  Stand-pipes,"  and  referring  to  the  charac- 
ter of  joint,  suggests  some  points  where  there  is  room  for 
improvement.  He  writes  as  follows:  "  One  is  the  method  of 

142 


RIVETING. 


joining  the  plates.  The  present  method  of  lapping  both  hori- 
zontal and  vertical  seams  is  awkward  and  unmechanical,  and 
belongs  more  to  the  methods  of  the  village  blacksmith  than 
those  of  precise  and  scientific  mechanism.  They  should 
rather  be  like  the  accompanying  sketch,  taken  from  a  paper 
read  before  the  New  England  Water-works  Association  in 
1893. 

"  In  this  sketch  the  horizontal  seams  are  lapped,  and  the 
vertical  seams  made  with  butt-straps.     This  is  a  perfectly  pre- 


CALKING  JOINT. 


oic 


CALKING  JOINT-^ 


CALKING  JOIKTv^ 


?.QOOiO_O(j)_ogc  ggjoo 


FIG.  39. — METHOD  OF  JOINING  PLATES  IN  STEEL. 

cise  method,  and  requires  no  beating  down  or  drawing  out  of 
the  plates,  and,  in  my  opinion,  would  really  cost  no  more  than 
the  old  way.  I  use  it  now  on  plates  over  £  in.  in  thickness, 
but  should  prefer  to  use  it  on  all  thicknesses." 

Notwithstanding  Mr.  Coffin's  opinion  as  to  the  relative 
cost,  builders  of  stand-pipes  will  make  quite  a  difference  in 
the  cost  of  a  particular  structure  if  the  butt-joint  is  required, 
as  it  seems  perfectly  proper  that  they  should  do,  for  the  rea- 
son that  a  butt-joint  requires  twice  as  many  rivets  as  a  lap- 
joint,  because  in  the  lap  the  rivet  passes  through  both  the 
plates,  whereas  in  the  butt-joint  it  passes  through  only  one, 
so  that  there  is  necessarily  an  additional  cost  for  punching  or 
drilling,  rivets,  and  driving. 


144  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

There  is  no  question,  however,  as  to  the  increased  value 
of  a  joint  made  as  suggested  by  Mr.  Coffin  over  the  usual 
method,  and  it  would  seem  as  though  the  best  practice 
should  govern  where  the  whole  strength  of  the  structure 
may  depend  upon  its  method  of  being  assembled. 

Efficiency  of  Riveted  Joints.— The  "  efficiency  "  of  a  riv- 
eted joint  is  described  as  being  the  ratio  of  the  strength  of  the 
joint  to  that  of  the  solid  plate.  Thus,  a  joint  is  said  to  have 
a  7O-per-cent.  efficiency  when  the  loss  of  strength,  as  com- 
pared with  its  ultimate  strength,  is  30  per  cent. 

In  order  to  determine  the  efficiency  of  a  riveted  joint,  it  is 
necessary  to  know  or  to  assume  the  following  conditions : 

(i)  The  tensile  strength  of  the  plate.  (2)  The  diameter 
of  the  rivets  used.  (3)  The  unit  resistance  of  these  rivets, 
and  their  "  pitch  "  or  spacing,  taken  from  centre  to  centre. 

When  proper  values  have  been  determined  for  the  forego- 
ing conditions,  it  has  been  found  by  practical  tests  and  demon- 
strations that  the  efficiency  of  the  several  joints  is  approxi- 
mately as  follows : 

Single-riveted  joint 56  per  cent.  eff. 

Double-   "  "     69    "       " 

Triple-     •'  "     75    " 

Double- welt  butt-joint 87    "       "       " 

Quadruple-riveted  butt-joint..  95    "       "       " 

One  of  the  most  interesting  and  practical  discussions  of  the 
theory  and  practice  of  riveting  with  which  the  author  is 
familiar,  is  contained  in  an  address  delivered  to  the  students 
of  Cornell  College  by  Mr.  J.  M.  Allen,  president  of  the 
Hartford  Steam  Boiler  and  Insurance  Co.,  and  from  which  is 
quoted  the  following: 

Single-riveted  Joints  (Fig.  40). — "In  calculating  the 
strength  of  a  single-riveted  joint  we  must  know,  first,  what 
the  tensile  strength  of  the  iron  or  steel  plate  is,  from  tensile 


RIVETING.  145 

test ;  second,  the  diameter  and  pitch  of  the  rivets ;  and  third, 
the  resistance  to  shearing  per  square  inch  of  the  material  of 
which  the  rivets  are  made.  On  this  latter  requirement  there 
has  been  no  little  discussion.  It  was  formerly  assumed,  when 
only  iron  plates  and  iron  rivets  were  used,  that  the  shearing- 
resistance  of  a  square  inch  of  rivet  was  equal  to  the  tensile 
strength  of  a  square  inch  of  the  rivet  itself  or  of  the  plate. 
That  is,  if  we  have  iron  of  a  tensile  strength  of  45,000  Ibs.  per 
square  inch,  the  shearing-resistance  of  a  square  inch  of  rivet 
would  be  45,000  Ibs.  On  this  assumption  it  would  be  only 
necessary  to  so  arrange  the  diameter  and  pitch  of  rivets  that 


FIG.  40. — SINGLE-RIVETED  JOINT. 

the  area  of  the  rivet  or  rivets  to  be  sheared  should  exactly 
equal  the  net  section  of  plate  to  secure  a  perfect  joint.  Later 
experiments,  together  with  the  improvements  in  the  manu- 
facture of  iron,  and  the  introduction  of  steel,  have  changed 
these  conditions  relatively.  While  the  shearing-resistance  of 
the  rivets  per  square  inch  has  been,  and  even  to-day  is,  by 
many  assumed  to  be  45,000  Ibs.  per  square  inch,  the  assump- 
tion has  arisen,  no  doubt,  from  the  fact  that  rivets  rarely  shear. 
I  have  examined  many  exploded  boilers,  and  the  fractures 
have  almost  invariably  been  through  the  solid  plate  or  along 
the  line  of  rivets.  It  is  very  rare  that  the  rivets  shear.  This, 
no  doubt,  arises  from  the  fact  that  the  pitch  of  the  rivets  was 
out  of  proportion  to  the  net  section  of  the  plate.  The  old  rule 
seemed  to  be:  the  more  rivets,  the  stronger  joint.  There 
was,  no  doubt,  a  desire  on  the  part  of  the  boiler-makers  to 


146  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

P 

make  a  tight  joint,  and  they  thought  that  if  they  pitched  the 
rivets  wider  it  would  be  difficult  to  caulk  the  joint  so  that  it 
would  be  steam-  and  water-tight. 

One  would  quite  naturally  assume  that  steel  plates  should 
be  riveted  with  steel  rivets,  but  such  is  not  the  usual  prac- 
tice. Most  of  the  boilers  now  constructed  in  this  country  are 
made  of  steel  plates,  and  they  are  largely  riveted  with  iron 
rivets.  In  this  country  there  have  been  comparatively  few 
experiments  on  the  strength  of  riveted  joints  made  of  steel 
plates  and  steel  rivets,  and  as  the  general  practice  is  to  use 
iron  rivets  with  both  iron  and  steel  plates,  I  confine  myself 
here  to  the  discussion  of  the  iron  rivet.  I  will  say,  however, 
that  in  England  very  careful  experiments  have  been  made, 
and  a  large  percentage  of  strength  is  given  to  steel  rivets  over 
iron  rivets.  When  the  true  value  of  the  steel  rivet  is  fully 
decided,  and  its  use  becomes  general  in  this  country,  that 
value  can  be  easily  substituted  for  the  value  of  iron  rivets  in 
the  calculations  of  the  strength  of  riveted  joints,  the  other 
elements  of  the  problem  remaining  the  same. 

What  value,  then,  shall  we  give  to  the  iron  rivets  when 
used  in  connection  with  steel  or  iron  plates?  In  settling  this 
question,  I  have  not  only  been  aided  by  the  experiments  of 
English  engineers,  but  I  have  availed  myself  of  experiments 
made  on  the  large  Emery  testing-machine  at  the  U.  S.  Ar- 
senal at  Watertown,  Mass.  These  experiments  have  been 
made  with  American  iron  and  steel,  and  hence  will  be  valu- 
able to  us  all  in  our  practical  work  in  this  country.  In  a 
series  of  five  experiments  with  steel  plates  and  iron  rivets, 
holes  punched,  the  shearing-resistance  per  square  inch  was  as 
follows:  39,740  Ibs.,  38,190  Ibs.,  36,770  Ibs.,  38,638  Ibs., 
and  41,100  Ibs.  In  view  of  these  results,  and  other  similar 
experiments,  I  assume  38,000  Ibs.  per  square  inch  as  the  safe 
estimate  of  the  single  shearing-resistance  of  iron  rivets  in 
steel  plates.  Later  experiments  may  change  these  figures 


RIVETING.  147 

slightly.  In  these  experiments  the  steel  plate  was  55,000 
Ibs.  tensile  strength  per  sq.  in. 

Assuming  38,000  Ibs.  as  the  safe  estimate,  we  must  de- 
cide upon  the  thickness  of  plate,  diameter  of  rivet-hole,  and 
pitch  of  rivets.  In  deciding  upon  these  elements  in  the  prob- 
lem, we  must  so  adjust  the  size  and  pitch  of  rivets  as  to  make 
the  shearing-resistance  of  the  rivets  as  near  the  strength  of 
net  section  as  possible.  I  will  assume  the  elements  of  the 
problem  to  be  as  follows : 

Steel  plate,  tensile  strength  per  square  inch  of  section, 
55,000  Ibs. 

Thickness  of  plate  T5T  in.  =  decimal  0.3125. 

Diameter  of  rivet-hole  ||  in.  =  decimal  0.8125. 

Area  of  rivet-hole  =  decimal  0.5185. 

Pitch  of  rivets  if  ins.  ^decimal  1.875. 

Shearing-resistance  of  iron  rivets  per  square  inch  =  38,000 
Ibs. 

Then  1.875  X  0.3125  X  55,ooo  =  32,226  Ibs.  =  strength 
of  solid  plate. 

(1.875  —  0.8125)  X  0.3125  X  55,ooo  =  18,262  =  strength 
net  section  of  plate. 

0.5185  X  38,000=  19,703  Ibs.  =  strength  one  rivet  in 
single  shear. 

Net  section  of  plate  is  the  weakest,  therefore  18,262  -f- 
32,226  =  56.6  per  cent,  efficiency  of  joint. 

Double-riveted  Joints  (Fig.  41). — In  double-riveted  joints 
we  find  an  accession  of  strength  over  single-riveted  joints  of 
nearly  20  per  cent.  This  arises  from  the  wider  lap  and  the 
better  distribution  of  the  material.  The  rivets  are  pitched 
wider,  and  there  is  more  rivet-area  to  be  sheared,  together 
with  a  larger  percentage  of  net  section  of  plate  to  be  broken. 

Steel  plate,  tensile  strength  per  square  inch  of  section, 
55,000  Ibs. 


148  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

Thickness  of  plate  f  in.  =  decimal  0.375. 

Diameter  rivet-hole  \\  in.  =  decimal  0.9375. 

Area  of  rivet-hole  =  decimal  0,69. 

Pitch  of  rivets  3^  ins.  =  decimal  3.0625. 

Shearing-resistance  of  iron  rivets  per  square  inch,  38,000 
Ibs. 

Then  3.0625  X  0.375  X  55,000  =  63,164=  strength  of 
solid  plate. 

(3.0625  —  0.9375)  X  0.375  X  55»ooo  =  43,828  Ibs.  = 
strength  of  net  section. 

0.69  X  2  X  38,000  =  52,440  Ibs.  =  strength  of  two  rivets 
in  single  shear. 

Net  section  of  plate  is  the  weakest,  therefore  43,828  -5- 
63,164  =  69.3  per  cent,  efficiency  of  joint. 

70  per  cent,  is  usually  assumed  in  practice. 


FIG   41. — DOUBLE-RIVETED  JOINT. 

Triple-riveted  Joint  (Fig.  42). — In  a  triple  lap-riveted  joint 
we  still  gain  in  strength  for  reasons  similar  to  those  above. 

Steel  plate,  tensile  strength  per  square  inch  of  section, 
55,000  Ibs. 

Thickness  of  plate  -f-  in.  =  decimal  0.375. 

Diameter  of  rivet-holes  if  in.  =  decimal  0.8125. 

Area  of  rivet-hole  =  decimal  0.5185. 

Pitch  of  rivets  3^  ins.  =  decimal,  3.25. 

Shearing-resistance  of  iron  rivets  per  square  inch,  38,000 
Ibs. 


RIVETING. 


149 


Then  3.25  X  0.375  X  55»ooo  =  57,031  Ibs.  =  strength  of 
solid  plate. 

(3.25  -  0.8125)  X  0.375  X  55,ooo  =  50,273  Ibs.  = 
strength  of  net  section  plate. 

0.5185  X  3  X  38,000  =  59,109  Ibs.  =  strength  of  3  rivets 
in  single  shear. 

Net  section  of  plate  is  weakest,  therefore  50,273  -f-  67,031 
=  75  per  cent,  efficiency  of  joint. 


FIG.  42. — TRIPLE- RIVETED  JOINT. 

Double-welt  Butt-joint  (Fig.  44). — We  now  come  to  the 
double-welt  butt-joint,  triple-riveted. 

I  have  selected  this  joint  because  we  use  it  in  practice  where 
boilers  of  large  diameters  and  high  pressures  are  required. 

In  the  double-welt  joint  a  new  element  comes  into  the 
problem,  viz.,  that  of  rivets  in  double-shear.  Its  inner  welt  is 
broader  than  the  outer  welt,  and  extends  far  enough  beyond  the 
former  to  enable  us  to  introduce  a  third  row  of  rivets,  which 
are  in  single-shear,  but  also  are  in  double-pitch.  This  in- 
creases the  net  section  of  plate,  and  also  adds  another  rivet  to  be 
sheared.  All  the  other  rivets  are  in  double-shear.  The  ques- 
tion now  arises,  What  is  the  value  of  a  rivet  in  double-shear? 
We  have  assumed,  therefore,  that  the  value  of  a  rivet  in 
single-shear  was  38,000  Ibs.  per  square  inch. 

Now,  can  we  assume  that  the  same  rivet  in  double-shear 
has  twice  the  value  that  it  had  in  single-shear?  It  has  been 


150  TOWERS  AND    TANKS   FOR    WATER-WORKS. 

assumed  by  some  writers  that  such  is  the  case,  and  up  to  this 
time  most  engineers  allow  a  double  value  to  rivets  in  double- 
shear.  In  the  former  the  rivet  is  sustained  by  the  plates 
above  and  below,  while  in  single-shear  the  resistance  is  con- 
fined to  one  point. 

An  examination  of  the  sheared  sections  of  rivets  in  single- 
shear  usually  discloses  a  slight  elongation  in  the  direction  of 
the  force  applied.  The  experiments  on  rivets  in  single-shear, 
and  from  which  we  get  our  data,  have  almost  always  been  made 
on  single-riveted  joints,  with  narrow  strips  of  iron,  as  shown 
in  Fig.  43. 


FIG.  43- 

And  it  is  reasonable  to  assume  that  there  is  a  slight 
tendency  in  the  rivet  to  lean  in  the  direction  of  the  force  ap- 
plied, which  would  account  for  the  slight  elongation  of  the 
sheared  section  in  that  direction.  An  examination  of  the 
sheared  sections  of  rivets  in  double-shear  shows  little  or  no 
elongation.  The  rivets  being  supported  by  the  plates  above 
and  below,  the  shear  is  direct,  and  the  section  is  normal  in 
form.  Experiments  made  by  the  English  Admiralty  with  f- 
inch  rivets  showed  that  the  double-shear  was  about  90  per 
cent,  stronger  than  the  same  diameter  of  rivet  in  single-shear. 
Chief  Engineer  Shock,  U.S.N.,  found  by  experiment  that 
the  resistance  of  bolts  of  iron  to  single-shear  was  40,700  Ibs. 
per  square  inch,  and  in  double-shear  75,300  Ibs.  This 
gives  an  increase  of  strength  of  85  per  cent.  The  results 
of  numerous  experiments,  both  in  this  country  and  in  Europe, 
show  the  resistance  to  double-shear  to  be  from  85  to  90  per 
cent,  greater  than  the  same  rivets  in  single-shear.  From  the 
foregoing  I  assume  85  per  cent,  as  a  fair  and  safe  estimate  of 


RIVETING.  151 

the  excess  of  strength  of  rivets  in  double-shear  over  those  in 
single-shear.  We  have  already  assumed  that  the  resistance  of 
rivets  per  square  inch  to  single-shear  is  38,000  IBs.  If  we 
add  to  this  85  per  cent.,  we  shall  have  70,300  Ibs.  as  the  safe 
estimate  of  the  resistance  of  iron  rivets  per  square 'inch  to 
double-shear.  Further  experiments  may  change  these  fig- 
ures slightly,  but  I  regard  them  as  safe  for  use  in  all  places 
where  joints  riveted  with  iron  rivets  are  used.  The  use  of  the 
double-welt  butt-joint  in  the  construction  of  boilers  is  becom- 
ing quite  common.  This  arises  from  the  use  of  boilers  of 
much  larger  diameter  than  those  formerly  used,  and  also  the 
necessity  for  higher  pressures  on  account  of  the  introduction 
of  compound  engines. 

With  larger  diameter  and  higher  pressures,  we  find  our- 
selves confronted  with  a  very  important  problem.  We  must 
keep  within  the  bounds  of  safety,  for  these  large  vessels  are 
very  destructive  to  life  and  property  if  we  disregard  the  im- 
portance of  good  material,  good  workmanship,  and  the  well- 
established  factors  of  safety.  It  is  not  always  safe  to  assume 
the  highest  results  obtained  by  experimental  tests.  There 
will  always  be  those  who  will  insist  upon  higher  pressures  than 
safe  rules  will  allow.  Hence  it  becomes  important  that  the 
consulting  engineer  shall  thoroughly  understand  the  principles 
of  safe  construction,  and  not  allow  himself  to  be  moved  in  his 
judgment  where  the  question  of  safety  is  involved.  We  will 
now  apply  the  above  data  to  the  following  problem : 

Steel  plate,  tensile  strength  per  sq.  in.  of  section, 5 5,000 Ibs. 

Thickness  of  plate  f  in.  :=  decimal  0.375. 

Diameter  of  rivet-holes  ||  in.  =  decimal  0.8125. 

Area  of  rivet-hole  =  decimal  0.5185. 

Pitch  of  rivets  in  inner  rows'3^  ins.  =  decimal  3.25. 

Pitch  of  rivets  in  outer  rows  6J  ins.  =  decimal  6.50. 

Resistance  of  rivets  in  single-shear  =  38,000  Ibs.  ^ 

Resistance  of  rivets  in  double-shear  =  70,300  Ibs. 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 


6-5  X  0.375  X  55,000=  134,062  Ibs.  =  strength  of  solid 
plate. 

(6.5  —  0.8 125) x  0.375  X  5 5, ooo  =  1 1 7, 304  Ibs.  =  strength 
of  net  section  of  plate  at  AB. 

0.5185  X  4  X  70,300=  145,802  Ibs.  =  strength  of  4  rivets 
in  double-shear. 

0.5185  X  38,000=  19,703  Ibs.  =  strength  of  I  rivet  in 
single-shear. 

This  last  result  must  be  added  to  the  strength  of  four 
rivets  in  double  shear — thus,  145,802  -|-  19,703  =  165,505  = 
shearing-strength  of  all  the  rivets.  The  net  section  of  plate 


FIG.  44.  — DOUBLE-WELT  BUTT-JOINT. 

is    weakest;    therefore,    117,304—134,062  =  87.5   percent. 

efficiency  of  joint. 

It  will  no  doubt  be  observed  that  the  strength  of  rivets  in 

this  joint  is  largely  in  excess  of  the  strength  of  net  section  of 

plate,  and  the  question  will  arise,  Why  increase  the  width  of 
inner  covering-strip  and  add  two  more  rivets?  As  stated 
ve,  this  was  done  to  increase  the  net  section  of  plate  at  AB, 


aW 


RIVETING. 


153 


and  thus  increase  the  efficiency  of  the  joint.  If  the  inner  welt 
or  covering-strip  had  been  of  the  same  width  as  the  outer  one, 
the  net  section  of  the  plate  would  have  been  greatly  reduced, 
and  the  difference  of  strength  between  net  section  of  plates 
and  rivets  would  have  been  greater,  thus  reducing  the  effi- 
ciency of  joint.  The  problem  would  be  as  follows : 

6-5  X  0.375  X  55,ooo  =  134,062  =  strength  of  solid  plate. 

(6.5  —0.8125X2)  x  o.375X55>ooo  =  100,546  =  strength 
of  net  section  of  plate. 

0.5185  X  4  X  70,300  =  145,802  =  strength  of  4  rivets  in 
double  shear.  Net  section  of  plate  is  the  weakest;  therefore, 
100,546  -:-  134,062  =  only  75  per  cent,  efficiency  of  joint. 

Again,  it  may  be  suggested:  Why  not  dispense  with  one 
row  of  rivets  in  double  shear,  and  extend  the  inner  welt  or 
covering-strip  so  that  the  outer  row  of  rivets  in  double  pitch 
and  single  shear  could  be  used,  thus  increasing  net  section  of 
plate  as  in  the  original  problem,  but  reducing  at  the  same 
time  the  shearing-resistance  of  the  rivets? 

The  solution  of  this  problem  would  be  as  follows: 

6-5  X  0.375  X  55.000  =  134,062  =  strength  of  solid 
plate. 

(6.5  -0.8125)  X  0.475  X  55>ooo  =  117,304  =  strength  of 
net  section. 

0.5185  X  2  X  70,300  =  72,901  =  strength  of  2  rivets  in 
double  shear. 

0.5185  X  38,000=  19,703  =  strength  of  i  rivet  in  single 
shear. 

This  last  result  must  be  added  to  the  result  of  2  rivets  in 
double  shear.  72,901  -f-  11,703  =  92,604  =  strength  of  all 
the  rivets. 

The  total  strength  of  the  rivets  is  the  weakest ;  therefore, 
92,604  -f-  134,062  =  69  per  cent,  efficiency  of  joint. 

It  may  be  further  suggested  that  a  rivet  of  smaller  diame- 
ter could  be  used.  I  will  say  that  I  have  also  considered  such 


154  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

a  problem,  but  have  come  to  the  conclusion  that  the  joint,  as 
illustrated  and  described,  for  efficiency  and  freedom  from 
leaks,  is  best.  I  will  say  here  that  a  joint  of  this  descrip- 
tion was  carefully  made  and  tested  on  the  Emery  machine  at 
the  United  States  Arsenal  at  Watertown,  Mass.  The  result 
of  the  test  was  two-twentieths  of  I  per  cent,  of  the  calculation 
made,  and  the  line  of  fracture  was  through  the  net  section  of 
plate  at  the  outer  row  of  rivets,  as  we  had  predicted." 

Since  the  lecture  delivered  by  Mr.  Allen,  in  1891,  there  has 
been  rapid  progress  both  in  the  manufacture  and  use  of  steel 
for  structural  purposes,  and  the  practice  of  uniting  steel  plates 
with  steel  rivets  has  become  the  rule  rather  than  the  excep- 
tion, although  it  seems  that  the  great  majority  of  metal- 
workers continue  to  be  very  conservative  in  assuming  higher 
shearing-values  for  steel  rivets,  and  while  the  steel  rivet  is  used, 
calculations  are  made  upon  its  efficiency  without  assuming 
much  higher  values  than  it  has  been  the  practice  to  give  to 
iron  rivets  subject  to  shear. 

In  1896  the  United  States  Government  made  a  series  of 
tests  upon  riveted  joints  at  the  Watertown  Arsenal.  These 
experiments  were  made  on  joints  formed  of  steel  plate,  and 
both  iron  and  steel  rivets. 

An  investigation  of  the  reports  shows  the  average  shear- 
ing-value of  steel  rivets  to  have  run  as  high  as  55,000  Ibs. 
per  square  inch  for  rivets  of  f-in.  and  J-in.  diameters,  and 
about  45,000  Ibs.  for  steel  bolts  under  the  same  condi- 
tions. 

From  these  tests  it  would  seem  that  the  shearing-value  of 
rivets  in  single-shear  was  about  the  same  as  the  ultimate 
strength  of  steel  rods  under  tension ;  and  it  would  therefore 
seem  that  a  higher  working  value  for  rivets  might  be  estab- 
lished, and  that  for  rivets  in  single-shear  an  ultimate  value  of 
45,000  to  50,000  Ibs.  per  square  inch  of  metal  would  not  be 
radical  or  likely  to  prove  unsafe. 


RIVETING. 


155 


As  has  been  shown,  if  the  plate  and  rivet  be  given  the  same 
values,  it  would  only  be  necessary  to  so  arrange  the  diameter 
and  pitch  of  rivet  that  the  area  of  the  rivets  should  equal  that 
of  the  net  section  of  plate  to  secure  a  perfect  joint,  but  the 
ultimate  value  of  plate  steel  is  about  60,000  Ibs.,  and  that  of 
rivet  metal  50,000  Ibs.  per  sq.  in.,  and  practice  has  further 
increased  the  difference  between  the  metals  by  allowing  only 
about  40,000  Ibs.  ultimate  strength  to  rivet-rods  under  shear. 

The  area  of  the  rivet-hole  represents  the  true  section  of 
the  rivet  when  driven,  and  therefore  the  area  of  the  rivet-hole, 
multiplied  by  the  shearing-value  of  the  metal,  gives  the 
strength  of  the  rivet. 

The  pitch  of  the  rivet,  representing  a  section  of  plate, 
multiplied  by  its  thickness  and  the  tensile  strength  of  the 
metal,  gives  the  strength  of  the  solid  plate,  while  the  pitch 
of  the  rivet,  or  length  of  section,  less  one-//#//"  the  diameter  of 
the  rivet-hole  at  each  end  of  the  section,  or  for  both  ends, 
the  diameter  of  the  rivet-hole,  multiplied  by  the  thickness  of 
the  plate  and  its  ultimate  tensile  strength,  will  give  the 
strength  of  the  net  section  of  plate.  The  relation  of  these 
values  expressing  the  '  '  efficiency  "  of  the  joint  in  per  cent,  is 
therefore  found  by  dividing  the  greater  value  by  the  least. 

Pitch  of  Rivets.  —  The  pitch  of  the  rivet  is  found  by  the 
formula 

A  x  S 


P=  Pitch  of  rivet, 

A  =  Area  of  rivet-hole  in  decimal  of  an  inch, 
S  =  Shearing-value  of  rivet, 
T  =  Thickness  of  plate, 
Q  —  Tensile  strength  of  plate, 
D=  Diameter  of  rivet-hole  in  inches. 

Where   rivet   is    in   more  than   single  pitch,  multiply   by 
number  of  rivets  in  row. 


156 


TOWERS   AND    TANKS  FOR    WATER-WORKS. 


Example.- — Find  the  proper  pitch  for  double-riveted  joint, 
in.  plate  and  f-in.  rivet : 

3712  X  2  X  40*000 


P= 


.6875  =  2.6671  or  2f  in. 


.2500  X  60,000 

In  the  example  above,  40,000  Ibs.  is  taken  as  being  a  con- 
servative value  for  a  rivet  in  single-shear,  and  as  allowing  some 
latitude  for  irregularity  in  shop-work. 

Size  of  Rivets  in  Relation  to  Thickness  of  Plates. — The 
determination  of  the  size  of  rivet  to  be  used  as  a  fastener  for 
certain  thicknesses  of  plates  is  not  governed  by  any  hard  and 
fast  rule,  but  varies  considerably  in  the  practice  of  different 
manufacturers. 

From  investigation  made  by  the  United  States  Govern- 
ment, the  relation  of  thickness  of  plates  to  diameter  and  length 
of  rivets  has  been  established  by  the  Bureau  of  Construction 
and  Repair,  Navy  Department,  as  follows: 


Thickness  of  Plate, 
Inches. 

Diam.  of  Rivet. 

Corresponding  Rivet-hole 
Area. 

Length, 
Inches. 

In. 

Dec. 

In. 

Dec. 

1 

1 
I 

I 

•3750 
.5000 
.6250 
.7500 
.8750 
I.  0000 

i 

ii 

•4375 
•  5625 

.6875 

.8125 

•9375 
1.6250 

•1503 

.2485 
.3712 
•  5185 
.6903 
1.0031 

1 

I 

Ii 
If 

3 

8    to   4-    . 

*  »£    :      . 

i  ..  Y.. 

V  "  1 

I  "I  ... 

4s 

[NOTE. — Centres  of  rivets  are  spaced  not  less-than  if  times  their  diam- 
eter from  the  edges.  In  double-  and  treble-riveting,  their  distance  from 
centre  to  centre  of  rows  (horizontal  pitch)  to  be  not  less  than  2^  diameters 
in  laps,  and  2^  diameters  for  straps.] 

In  the  above  table  the  length  includes  length  of  shank 
necessary  to  form  the  field-head  measured  under  manufactu- 
rers' head,  and  for  a  ''grip"  equal  to  twice  the  thickness  of 
plate  assumed. 

In  order  to  facilitate  calculations  for  water-tight  metallic 
joints,  the  following  table,  providing  an  efficiency  of  joint  suit- 
able for  metallic  reservoirs,  and  an  auxiliary  diagram  of 
details,  has  been  designed  by  the  author. 


RIVETING. 


157 


DIMENSIONS    OF    LAPS    USING    %    RIVETS. 


LAPS    USING   M" RIVETS. 


LAPS  USING  %"RIVETS. 


BUTT  STRAP-%"RIVETS. 
FIG.  45. 


I58 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 


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RIVETING. 


159 


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160  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

The  sizes  and  spacing  of  rivets  for  marine-,  boiler-,  and 
tank-work,  requiring  water-  and  steam-tight  joints,  is  some- 
what different  from  that  demanded  for  structural  work,  such 
as  bridges,  buildings,  and  towers.  For  structures  of  the  latter 
type,  the  following  general  rules  are  applicable : 

RIVET-SIZES    AND    SPACING    FOR   STRUCTURAL   WORK. 
(DU    BOIS.) 

Diameter  of  rivet-hole  :  Not  less  than  thickness  of  thickest 
plate  through  which  it  passes.  For  cross-girders,  stringers, 
compression-members :  {-  to  J-in.  rivets. 

General  rule:    Diameter  of  hole  =  ij  thickness -j- T3^-  in. 

Number  of  rivets:  Divide  total  stress  transmitted  by  joint 
by  product  of  diameter  of  rivet  by  thickness  of  plate  by  safe 
bearing-value  per  square  inch  of  rivet  material. 

For  number  of  rivets  to  resist  shear:  Divide  total  stress 
by  product  of  area  of  rivet,  by  safe  shearing-value.  (Shearing- 
values  used  in  practice  are  6000  to  7000  Ibs.  per  square  inch.) 

RIVET-SPACING    FOR     STRUCTURAL    WORK. 

Assume  shearing  strength  equal  to  tensile  strength. 

/  =  pitch ;    d  =  diameter  of  rivet ;    /  =  thickness  of  plate, 

a 
and  a  =  section  of  rivet.      /  =  — 

Practical  restrictions :  Rivets  should  not  be  closer  than  3 
diameters,  nor  more  than  6  inches,  centre  to  centre.  In  com- 
pression, never  more  than  16  times  thickness  of  thinnest  out- 
side plate.  Distance  from  centre  of  rivet-hole  to  edge,  end, 
or  next  row  of  rivets  should  not  be  less  than  2  diameters  of 
rivet.  The  following  table  is  the  Carnegie  Steel  Company's 
practice  for  structural  work : 


RIVETING. 


161 


NGES  OF  if-C 


VETS  FOR 


CARNEGIE  STANDARD  SPACING  AND  DIMENSIONS  OF 


FOR 

S  & 


°0 


JR  :* 


ING 


THOD  OF  INCR 
SECTION  AR 


-?!*    K, 


V\l 


7/16" 


-  % 


IS 


ij- 

For 


•  ^   ^ 


CHAPTER   VIII. 
DESIGNING. 

HAVING  formed  a  clear  conception  of  the  principles  ex- 
plained in  the  preceding  chapters,  it  is  possible  to  consider 
intelligently  the  subject  of  designing  metallic  reservoirs  and 
their  supporting  substructures. 

By  the  use  of  the  various  tables,  applicable  to  included 
sizes,  the  study  of  suitable  design  is  greatly  facilitated  and 
simplified.  In  the  general  scheme  of  a  water-supply  system, 
where  storage  and  gravity  supply  is  included,  in  the  absence 
of  a  sufficiently  elevated  natural  location,  the  necessity  for 
some  form  of  metallic  reservoir  to  supply  or  supplement  the 
deficiency  is  apparent. 

From  the  general  requirements  as  to  pressure  and  storage, 
the  dimensions  of  the  structure  will  be  determined. 

From  the  analysis  of  " Stand-pipe  Statistics,"  page  8,  it 
has  been  found  that  the  average  domestic  pressure,  as  required 
in  the  United  States,  is  61.2  Ibs.'per  sq.  inch.  If  this  pres- 
sure is  satisfactory  to  the  designing  engineer,  as  shown  on 
page  65,  the  corresponding  height  or  head  is  approximately 
142  ft.,  which  would  be  the  required  height  of  the  stand-pipe. 
Under  ordinary  conditions,  however,  the  local  topographical 
condition  is  likely  to  afford  certain  convenient  natural  eleva- 
tions, advantage  of  which  may  be  taken  to  reduce  the  height 
of  the  metallic  reservoir,  which  height,  supplemented  by  the 
natural  elevation,  will  give  the  required  pressure. 

In  the  case  of  a  particular  design,  where  there  occurs  an 

162 


DESIGNING.  163 

available  natural  elevation  of  22  or  23  ft.,  representing  a  pres- 
sure of  say  10  Ibs.,  the  difference  between  this  and  the  re- 
quired pressure  of  61.2  Ibs.  is  51.2,  and  which  we  see  (page 
65)  represents  a  head  of  120  ft.  approximately;  and  we  there- 
fore determine  to  erect  a  stand-pipe  120  ft.  in  height,  and, 
having  assumed  the  height,  the  capacity  required  fixes  the 
dimensions. 

The  question  of  capacity  is  settled  most  arbitrarily;  but, 
in  general,  it  is  the  usual  practice  to  provide  a  storage  or 
reserve  supply  which  will  permit  the  temporary  stoppage  of 
the  pumping-engines  for  repairs,  etc.,  for  a  given  number  of 
hours.  In  small  towns,  particularly  where  a  lighting-plant 
may  be  operated  in  conjunction  with  the  water-works,  it  is 
sometimes  deemed  desirable  to  provide  sufficient  storage  to 
supply  the  ordinary  consumption  during  the  day  by  the  pump- 
ing done  at  night,  making  only  one  set  of  firemen  and 
engineers  necessary  for  both  plants.  Another  determining  ele- 
ment in  fixing  the  capacity  of  storage  and  the  corresponding 
size  of  the  reservoir  is,  of  course,  the  item  of  cost  and  the 
amount  of  money  available.  As  has  been  shown,  the  widest 
range  of  practice  in  the  matter  of  diameter,  height,  and  cor- 
responding capacity  exists;  but,  for  the  purpose  of  discussion 
and  analysis,  we  will  assume  that  a  metallic  reservoir  of 
400,000  U.  S.  gals,  is  required.  The  height  having  been 
taken  as  120  ft.,  from  the  table  (page  95),  we  see  that,  for  the 
given  height  and  capacity,  the  diameter  will  be  approximately 
24  ft.,  the  actual  capacity  for  the  cylinder,  120  X  24  ft.,  being 
407,150  U.  S.  gallons. 

Strain-sheet. — In  designing  such  a  structure,  through  the 
employment  of  the  principles  previously  enunciated,  the 
details  can  be  specified  ;  their  correctness  demonstrated  mathe- 
matically, or  shown  graphically. 

Usually  a  graphic  demonstration  of  the  correct  principles 
of  construction  is  shown  by  a  "strain-sheet,"  similar  to  that 


164 


TOWERS   AND    TANKS  FOR    WAITER-WORKS. 


shown  below.  .  .  .  The  line  H ' B  is  first  drawn,  at  right 
angles  to  which  the  vertical  line  HH  is  laid  off.  By  any  con- 
venient scale,  point  off  or  divide  the  horizontal  and  vertical 
lines  into  equal  subdivisions. 


65 


30 


10 


\ 


\ 


\ 


\ 


\ 


\ 


\ 


\ 


\ 


\ 


\R 


\ 


H'  3/16  Y*  5/16  3/8  /16  '/2  9/l6  6/3  %          H 

FIG.  47. — STRAIN-SHEET,  24  X  I20-FT.  STAND-PIPE. 

The  subdivisions  of  the  horizontal  line  can  be  taken  to 
represent  the  decimal  or  fractional  parts  of  an  inch,  the  latter 
being  usually  the  case,  as  the  thickness  of  steel  or  iron  plate 
is  generally  considered  in  fractions  of  an  inch.  The  value  to 
be  given  the  horizontal  subdivision  will  depend  upon  the  in- 
tentions of  the  designing  engineer;  that  is,  whether  he 


DESIGNING.  165 


intends  to  construct  his  stand-pipe  of  plate  advancing 
32ds,  i6ths,  or  8ths  of  an  inch.  Usually  the  thickness  of  the 
plates  to  be  used  in  the  ascending  sections  or  rings  are  de- 
creased by  i6ths;  but,  in  close  calculations,  the  scale  is  taken 
at  32ds,  and  in  which  case  the  value  of  any  subdivision  would 
be  one  thirty-second  on  the  horizontal  line. 

The  value  given  to  equal  subdivisions  of  the  vertical  line 
H'H  can  be  taken  at  decimals  of  TOO  ft.,  and  represent  the 
height  of  each  panel  or  ring  taken  in  the  clear  —  that  is,  between 
laps.  The  height  of  the  rings  is  generally  uniform,  but  is 
entirely  arbitrary,  the  limiting  height  being  determined  by 
cost  and  convenience  of  handling;  thus,  a  stand-pipe  with 
a  greater  number  of  shorter  rings  would  require  a  greater 
number  of  connecting  joints,  with  increased  cost  of  rivets, 
punching,  and  driving,  as  well  as  decreased  efficiency  in  the 
general  strength  of  the  structure,  than  one  with  greater  height 
of  ring  and  fewer  joints;  but  the  larger  the  plate  which  is  to 
be  used  in  the  construction  of  the  ring,  the  more  difficult  it 
becomes  to  handle,  both  on  account  of  the  increased  weight 
and  the  trouble  given  by  the  wind  catching  the  broad  expanse 
of  plate  metal,  swinging  and  swaying  it  in  the  most  trouble- 
some manner  as  it  is  being  hoisted  into  place. 

It  has  been  found  from  practice,  both  in  shop-  and  field- 
work,  that  a  5  -ft.  segment  is  a  very  convenient  height,  and 
therefore  the  practice  of  making  the  rings  5  ft.  in  the  clear 
seems  to  be  in  general  use.  Assuming  that  this  height  will 
be  adopted,  the  value  of  the  subdivisions  of  the  vertical  scale 
would  be  5  ft. 

The  increasing  height  on  the  vertical  scale,  in  multiples  of 
five,  is  usually  indicated  as  shown  on  the  strain-sheet,  as  is 
also  the  increasing  thickness  on  the  horizontal  scale,  advancing 
by  i6ths,  32ds,  etc.,  as  may  be  determined  in  advance. 

Application  of  Mechanical  Principles.  —  The  formula  for 
arriving  at  the  theoretical  thickness  of  plates  is  explained  on 


1 66  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

page  91,  and  calculations  suited  to  a  wide  range  of  heights 
and  diameters  of  metallic  cylinders  have  been  given,  so  that 
between  these  ranges  it  is  only  necessary  to  revert  to  the  tables 
to  find  the  required  theoretical  thickness  of  the  metal  in  frac- 
tions and  decimals  of  an  inch  corresponding  to  the  required 
height  and  capacity. 

Thickness  of  Plate. — Considering  a  24- ft.  X  i2O-ft.  stand- 
pipe,  the  theoretical  thickness  of  the  lower  plate  is  seen  to  be 
f  of  an  inch. 

Determining  to  advance  by  i6ths,  twelve  subdivisions  of  the 
horizontal  line  equal  £  of  an  inch  thickness  of  plate.  Draw 
the  diagonal  line  H'B,  which  is  a  line  which  indicates  the 
theoretical  thickness  of  the  plate  from  zero  at  H,  and  where 
the  thickness  and  strength  of  a  piece  of  letter-paper  is  capable 
of  resisting  the  pressure  of  the  water,  to  B,  where  J  of  an  inch 
of  steel,  having  a  tensile  strength  of  60,000  Ibs.,  with  a  factor 
of  safety  of  4,  and  a  rivet-efficiency  of  f  the  ultimate  strength 
of  the  plate,  is  required  to  safely  resist  the  hydrostatic  press- 
ure of  51.97  Ibs.  per  square  inch. 

From  the  subdivisions  of  the  vertical  line  H'H,  draw  per- 
pendicular lines  parallel  to  the  base-line,  with  a  distance 
apart  of  5  ft.  by  the  assumed  scale,  and  with  each  length  equal 
to  the  theoretical  thickness  of  the  plate,  measured  by  the  scale 
of  the  base.  The  length  of  these  lines,  representing  the  theo- 
retical thickness  of  the  plate,  can  be  determined  mathemati- 
cally by  the  formula  given,  or  from  the  table,  as  was  done 
when  establishing  the  thickness  of  the  lower  plate  ;  but,  to  sim- 
plify this  process,  the  length  of  each  horizontal  line  can  be 
determined  graphically  by  terminating,  that  line  at  the  inter- 
section formed  by  vertical  lines,  projected  from  the  scale  of 
the  base,  but  which  are  not  usually  indicated  except  to  com- 
plete the  parallelogram. 

If  the  parallelogram  as  thus  formed  lies  inside  of  the 
diagonal  line,  the  plate  of  which  it  is  intended  to  construct 


DESIGNING.  167 

the  ring  is  less  than  the  required  theoretical  thickness  de- 
manded by  the  formula  for  the  assumed  conditions.  If  the 
parallelogram  projects  beyond  the  diagonal,  the  plate  has 
greater  thickness  and  strength  than  is  theoretically  necessary 
to  resist  the  hydrostatic  pressure  at  that  point,  the  projecting 
area  representing  the  excess  of  thickness  and  weight  of  the 
plate  metal,  and  to  that  extent  increasing  the  cost  of  the 
structure ;  in  the  same  way  the  area  included  in  the  section 
between  the  diagonal  and  the  vertical  line  when  the  latter  is 
within  the  diagonal  represents  the  proportion  of  insecurity. 
Obviously,  the  nearer  the  vertical  projected  line,  intersecting 
with  the  horizontal,  approaches  the  diagonal,  the  more  nearly 
are  the  theoretical  conditions  of  thickness  of  plate  to  applied 
pressure  complied  with  ;  hence,  in  graphic  design,  the  decrease 
in  thickness  of  plate,  corresponding  with  reduced  pressures, 
should  be  shown  as  rising  like  steps  along  the  diagonal,  the 
foot  of  each  rise  just  touching  the  diagonal  line,  and  the  three 
intersecting  lines  forming  triangles  whose  area  represents  the 
excess  of  strength  and  plate  metal  beyond  the  theoretical  re- 
quirements. This  will  be  clearly  understood  by  a  slight  study 
of  the  strain-sheet  on  page  164. 

Joint  Efficiency. — It  is  also  customary  to  indicate  upon  the 
strain-sheet,  graphically,  the  joint  efficiency,  or  the  percentage 
of  strength  of  the  joint  as  compared  with  the  strength  of  the 
plate,  showing  by  vertical  dotted  lines  in  each  section  the 
ratio  of  strength  which  the  specified  character  of  the  joint 
bears  to  the  strength  of  the  solid  plate. 

In  the  formula  for  determining  the  thickness  of  the  plate 
to  resist  safely  the  applied  pressures,  it  was  assumed  that  -J  of 
the  strength  of  the  plate  would  be  lost  by  punching  and  rivet- 
ing; hence  the  line  indicating  the  relative  efficiency  of  the 
joint,  or  the  "  rivet-efficiency  line,"  should  be  drawn  to  repre- 
sent 66.6  per  cent,  of  the  theoretical  strength  of  the  plate  as 
indicated  by  its  thickness  as  measured  on  the  scale  or  base-line  < 


1 68  TOWERS   AND    TANKS  FOR    WATER-WORKS. 

H'B.  Thus,  where  the  scale  of  the  base  is  taken  in  i6ths,  f 
of  an  inch  thickness  will  be  represented  by  twelve  subdivisions, 
which,  multiplied  by  66.6  per  cent.,  gives  7.99  as  the  distance 
of  the  point  where  the  rivet-efficiency  line  cuts  the  base  to  the 
point  H'. 

Draw  the  dotted  diagonal  H-R. 

For  each  ring  or  panel  the  distance  of  each  vertical  dotted 
line  from  the  dotted  diagonal  will  graphically  demonstrate  the 
excess  or  decreased  strength  of  that  particular  joint  more  or 
less  than  66.6  per  cent.  As  in  the  explanation  of  the  proper 
relation  of  plate  thickness  to  the  diagonal  theoretical  line  of 
strength,  so  the  dotted  vertical,  showing  rivet  efficiency  of 
the  particular  vertical  jpint,  should  not  fall  very  far  on  either 
side  of  the  66.6  per  cent. -rivet-efficiency  line  in  any  section  or 
ring;  otherwise  the  joint  will  be  too  weak  for  safety  in  the  one 
case  or  unnecessarily  strong,  entailing  increased  cost,  in  the 
other. 

It  has  been  previously  explained  how  the  efficiency  of  a 
riveted  joint  was  determined,  and  from  the  formula  deduced 
a  set  of  tables  has  been  calculated ;  it  is  therefore  only  neces- 
sary to  inspect  the  strength  and  efficiency  of  any  joint  as 
shown  in  the  table,  and  to  adopt  and  specify  the  character  of 
joint,  giving  the  requisite  percentage  of  strength  ;  then  for  any 
ring  or  section  whose  thickness  is  known  and  indicated  on  the 
vertical  scale,  multiply  the  number  of  subdivisions  represent- 
ing that  thickness  by  the  per-cent.  efficiency  of  the  accepted 
joint,  and  the  result  can  be  used  to  plot  the  point  where  the 
vertical  dotted  line  should  be  drawn,  as  was  done  to  establish 
the  point  R  on  the  base-line  H'B. 

The  strain-sheet  given  for  the  24-ft.  X  i2O-ft.  stand-pipe, 
and  further  above  explained  and  described,  is  frequently  more 
or  less  elaborated  to  include  other  details,  and  is  sometimes 
so  complete  as  to  render  further  specifications  unnecessary  for 
designing.  Further  details  for  this  stand-pipe  are  given  on 
the  following  page : 


DESIGNING. 


169 


DIMENSIONS    OF    LAPS    USING  %/XR.IVETS. 


LAPS    USING    M    RIVETS.  LAPS    USING   '%"RIVETS. 

DETAILS  OF  RIVETED  JOINTS. 


K  Plate 


DETAIL  OF  ANCHORAGE  CONNECTIONS.    1  O  LIKE  THIS.. 
FIG.    48. 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 

Bed-plate  and  Connections. — In  calculations  for  the  thick- 
ness of  the  4'  bed-plate  "  or  the  plate  which  is  to  form  the  bot- 
tom of  the  cylindrical  stand-pipe,  the  moment  of  the  weight  of 
the  column  of  water,  acting  through  the  centre  of  gravity 
and  applied  at  the  centre  of  the  circle,  would  be  found  by  mul- 
tiplying the  weight  by  its  leverage,  the  radius  of  the  circle, 
and  the  thickness  of  the  plate  to  resist  this  stress  would  be 
found  as  explained;  but  in  stand-pipes  the  bed  plate  rests 
upon  and  is  supported  by  the  subfoundation,  so  that  it  is  only 
necessary  to  provide  a  plate  which  can  be  satisfactorily  joined 
to  the  shell.  In  practice  where  the  shell-plate,  bottom  ring, 
is  \  in.  or  over  in  thickness,  the  thickness  of  the  bed-plate  is 
assumed  at  f  the  thickness  of  the  shell ;  where  the  bottom 
ring  is  less  than  £  in.,  the  bed-plate  is  taken  as  the  same 
thickness  as  the  shell.  In  large  stand-pipes  the  bed-plate 
sheets  are  cut  economically  to  represent  segments  of  the  circle, 
are  riveted  together  in  the  field,  and  joined  to  the  shell  by 
some  form  of  "  angle  "  or  "  L"  curved  to  radius.  The  length 
of  the  legs  of  the  angle  are  determined  by  the  character  of 
riveting  required,  sometimes  it  being  sufficient  to  single-rivet 
both  legs  to  the  shell-  and  bed-plate  respectively ;  sometimes 
the  shell  is  double-  and  the  bed-plate  single-riveted ;  some- 
times both  are  double-riveted,  hence  the  comparative  lengths 
of  the  angle-legs.  On  page  87  it  was  shown  that  the  maximum 

M 
bending  moment  per  square  inch  of  circumference  was  5  =  -,-, 

then  for  a  tank  24  ft.  diameter  by  120  ft.  in  height,  and  where 
the  dead  weight  or  weight  of  the  metal  is  roughly  85  tons, 
M  =  86,400X720  =  62,208,000  pounds-inches.  The  area  A  of 
the  tank  being  65,144  square  inches,  the  maximum  bending 

.    62,208,000 

stress  per  circumferential  inch  is  —r-  =955?  which  multi- 

°5'I44 

plied  by  its  leverage,  144  inches,  gives  165,024,  divided  by  the 
allowable  unit  stress  of  the  metal,  15,000,  gives  n  as  the  section 
modulus,  and  found  from  standard  section  tables  to  approx- 


DESIGNING.  171 

imate  an  angle  6  in.  x6  in.  by  T7ff  inches,  without  considering  the 
plate  of  which  the  tank  is  composed.  The  connecting- angle  n 
sometimes  placed  inside  and  sometimes  outside  of  the  cylinder, 
but  as  the  pressures  are  from  the  inside,  the  outside  angle  loca- 
tion is  preferred,  as  the  bed-plate  then  extends  beyond  the  shell, 
and  the  angle  riveted  on  acts  as  a  brace,  and  the  plate  and  leg 
of  the  angle  give  that  much  additional  stability  to  the  structure. 
Some  engineers  prefer  to  flange  the  shell-  and  bed-plate, 
making  a  flanged  joint  instead  of  the  angle-joint  as  described. 
Where  it  is  unnecessary  to  extend  the  area  of  the  base  by  the 
use  of  angles  and  web-plates,  and  the  simple  angles  are  used, as 
shown,  the  outer  arrangement  of  the  connecting-angle  is  impos- 
sible, and  the  connection  is  necessarily  made  on  the  inside. 

Details. — As  has  been  said,  the  hydrostatic  pressure  at  the 
top  of  a  tank  being  zero,  the  thickness  and  strength  of  a  sheet 
of  paper  would  be  sufficient  to  control  and  restrain  the  pres- 
sures and  water;  but,  in  stand-pipes  of  any  size,  the  thickness 
of  the  top  rings  is  usually  J  in.,  and  never  less  than  T3^  in. 
These  thicknesses  are  used  to  provide  for  the  weakening  of  the 
plates  by  oxidation  or  rusting  of  the  metal,  and  also  to  resist 
the  action  of  the  wind,  to  successfully  resist  which  it  is  usual 
to  provide  some  "  stiffener  "  at  the  top,  usually  an  angle  riv- 
eted to  the  inner  or  outer  circumference  of  the  cylinder,  the 
horizontal  leg  being  used  to  fasten  and  support  an  ornamental 
cresting,  generally  of  malleable  iron,  cast  in  segments,  and 
bolted  to  the  angle. 

In  the  record  of  stand-pipe  failures,  several  large  structures 
have  suffered  partial  or  total  collapse  during  high  winds,  the 
metal  being  rolled  up  at  the  top  into  a  cone  shape,  similar  to 
the  twisting  of  a  piece  of  paper  into  a  taper.  This  action  of 
the  wind  is  not  very  well  understood,  and  therefore  the  size  of 
the  stiffening  angle  customarily  placed  about  the  top  of  the  stand- 
pipe  is  generally  arbitrarily  assumed. 


TOWLRS  AND    TANKS  FOR    WATER-WORKS. 


^-Stiffening  Girder 


As  has  been  said,  at  the  top  of  the  tank  the  strain  from  the 
water  is  zero,  and  considering  the  cylinder  as  a  stack  under 
wind-pressure  the  vertical  components  of  the  uplift  may  be 
regarded  as  negligible,  and  there  remains  principally  the  con- 
sideration of  the  wind  normal  to  the  tank,  which  force  probably 
exercises  also  a  torsion  movement  and  is  also  known  to  produce 
a  vacuum  within  the  cylinder  and  on  the  leaward  side  of  the 
structure,  for  which  reasons  the  stresses  are  generally  considered 
as  indeterminate,  nor  is  it  possible  with  certainty  to  assume  the 
resistance  offered  by  the  shape,  which  is  probably  somewhere 
between  the  £rch  and  beam  action. 

The  effect  of  these  stresses  is  graphically  shown  on  page  28 
in  the  wreck  of  the  Lincoln,  Neb., 
stand-pipe,  whose  top  angle  was 
broken  and  the  shell  plates  were 
crumpled  up  for  some  40  feet  below 
the  top,  and  from  which  the  necessity 
for  making  suitable  provision  for 
wind- pressure  is  obvious. 

In  general  practice  a  lo-ft. 
diameter  tank  should  be  provided 
with  an  angle  not  less  than  4  in.  X4  in.;  a  2o-ft.  diameter  tank 
with  6  in.  x6  in.  angle,  and  for  pipes  of  larger  diameter  some 
.form  of  stiffening  girder,  and  which  might  also  be  utilized  as  a 
part  of  an  ornamental  design,  should  be  introduced. 

This  style  of  finish  for  the  top  of  a  stand-pipe,  while  in 
general  use,  is  subject  to  criticism  in  that  it  is  uncovered, 
and  in  some  waters  the  sunlight  quickly  forms  organic  growths, 
while  the  angle  without  the  cresting  is  an  inviting  roosting- 
place  for  birds — the  writer  having  seen  dozens  of  buzzards 
roosting  upon  the  tops  of  stand-pipes  so  constructed ;  again, 
in  cold  climates  an  uncovered  surface  is  objectionable  on 
account  of  the  greater  tendency  of  the  water  to  freezing,  sev- 
eral recorded  failures  being  ascribed  in  part  to  this  cause. 


DESIGNING.  173 

A  better  construction  is  to  provide  for  a  light  plate-metal 
cover,  supported  upon  radial  rafters  of  light  angle  or  channel 
shapes,  the  rafters  being  bent  to  project  vertically  below  the 
top  of  the  stand-pipe  and  forming  stiffeners  for  that  portion  of 
the  structure. 

In  addition  to  these  stiffeners  spaced  at  regular  intervals,  a 
light  horizontal  stiffener  should  be  provided,  set  12  or  1 8  inches 
below  the  top;  and,  if  a  Z  shape  is  specified,  a  suitable 
support  for  a  painter's  trolley  is  thus  secured,  which  will  be 
found  most  convenient! 

For  purposes  of  inspection  a  ladder  capable  of  safely  sus- 
taining a  weight  of  not  less  than  1000  Ibs.  should  be  designed, 
and  is  sometimes  used  both  inside  and  out — that  for  the  outside 
terminating  10  ft.  above  the  base  of  the  structure,  to  prevent 
mischievous  or  malicious  persons  from  having  too  ready  ac- 
cess to  this  facility.  Such  ladders  may  be  composed  of  two 
side-bars,  2  ins.  X  -fV  *n*>  w^^  i'm'  diameter  rungs  spaced 
12  to  1 8  inches,  which  may  also  be  a  suitable  spacing  for 
the  side-bars.  Such  ladders  are  generally  built  in  sections  at 
the  shop,  and  are  riveted  to,  the  sides  of  the  stand-pipe  at 
intervals  of  10  to  12  feet  with  light  angle-clips. 

As  it  is  sometimes  necessary  to  empty  the  stand-pipe  and 
to  remove  deposits,  it  is  necessary  to  provide  some  kind  of 
manhole  near  the  base,  which  is  usually  of  elliptical  form,  with 
plates,  arches,  and  bolts,  and  of  such  dimensions  as  to  provide 
easy  ingress  for  a  workman. 

A  suitable  connection  for  the  supply-pipe  must  also  be 
arranged  for,  its  dimensions  being  governed  largely  by  the 
size  of  the  inlet-pipe;  the  connection  is  usually  a  short  bell- 
mouth  section,  flanged  at  both  ends,  the  flange  to  be  in  con- 
tact with  the  plate  to  be  curved  to  radius  while  the  other  end 
is  planed  for  a  standard  flange-connection  with  the  inlet-pipe, 
the  first  section  of  which  generally  has  both  a  flange  and  bell 
end. 


174  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

Method  of  Anchorage. — Beside  those  above  described, 
suitable  connections  for  the  anchor  rods  must  be  designed  and 
the  number  and  size  of  the  rods  determined. 

The  method  and  formulae  given  at  length  on  page  87  are  of 
general  application. 

Analyzing  the  stresses  of  the  24  ft.  by  120  ft.  stand-pip? 
under  consideration,  we  find  from  rough  calculation  that  the 
weight  of  the  metal  or  the  "dead"  weight  is  some  85  ton;, 
hence  M  =  86,400x720  =62,208,000  pound-inches. 

The  area  A  of  the  tank  being  65,144,  the  maximum  bending 

_,     M         62,208,000 

stress  per  circumferential  inch  is  S  =— j-  or  — - —       — ,   gives 

A  65,144 

95 5 >  which  multiplied  by  the  length  of  the  arc  included  between 
the  anchor  rods  (assuming  10  to  be  sufficient,  and  spaced  alorg 
the  outer  circumference  of  the  tank,  but  sufficiently  removed  to 
allow  for  the  connection  and  for  the  use  of  a  tightening  wrench) 
and  to  an  assumed  radius  of  12  ft.  3  inches,  the  circumferential 
included  arc  would  be  92.4  inches  which,  when  multiplied  by  the 
unit  stress,  955,  would  produce  a  total  maximum  wind  reaction 
of  87,242  Ibs.  acting  on  any  one  rod.  The  weight  of  the  tank 
being  estimated  at  170,000  Ibs.,  the  net  stress  would  be  87,272, 
less  17,000  or  70,272  Ibs.,  which  divided  by  the  allowable  work- 
irg  stress  of  15,000  Ibs.  gives  a  cross-section  area  of  rod  equal  to 
4.685,  or  selecting  the  nearest  approximate  size,  the  required  rod 
would  be  2\  inches  in  diameter. 

Where  the  resultant  of  the  forces  passes  too  close  to  the  base 
it  is  frequently  considered  good  practice  to  add  stiffening  braces 
at  intervals  along  the  outer  circumference  of  the  tank.  These 
generally  consist  of  a  pair  of  angles  bent  to  bracket  form  with  a 
web  of  steel  plate  riveted  between.  These  braces  give  a  greater 
leverage  against  the  overturning  moment. 


DESIGNING. 


175 


TOWER  AND  TANK,  WEST  TAMPA,  FLA. 


CHAPTER  IX. 
DESIGNING— CONTINUED. 

IN  the  general  scheme  of  a  water-supply  plant,  where  storage 
is  required  and  to  be  obtained  only  by  the  erection  of  a  metallic 
reservoir,  it  is  sometimes  deemed  expedient  to  secure  a  suitable 
elevation  by  constructing  the  tank  upon  a  supporting  tower. 
Such  towers  are  made  in  many  ways  and  of  various  materials, 
brick,  wood,  and  metal  being  most  generally  used.  The  choice 
of  such  substructure  is  determined  by  the  conditions  of  capacity, 
cost,  and  local  surroundings. 

As  to  the  question  of  capacity,  the  same  considerations  apply 
as  those  explained  previously  for  stand-pipes. 

The  height  of  the  tank  superstructure  may  be  considered 
as  representing  the  minimum  and  maximum  desirable  or  limiting 
pressures,  hence  it  is  argued  that  a  stand-pipe  has  a  large  column 
of  water  which  is  useless  except  to  support  the  effective  head 
of  water  above  the  minimum  desirable  pressure  as  determined 
in  feet,  and  that  the  effective  column  may  be  more  economically 
supported  by  an  open  substructure,  such  as  a  steel  tower.  Argu- 
ments are  also  presented  that  the  lower  volume  of  water  in  a 
stand-pipe  being  useless  except  for  purposes  of  support,  it  is 
objectionable  from  the  fact  that  it  is  stagnant  and  the  greater 
volume  of  water  is  more  liable  to  be  affected  by  organic  growths. 
This  argument  is  controverted  upon  the  assumption  that  the 
temperature  of  the  water  is  constantly  changing  and  therefore 
all  sections  of  the  column  are  equally  fresh.  It  is  a  fact,  however, 
which  is  used  to  the  best  purposes  by  builders  of  this  type  of 

177 


178  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

structure,   that  the   record  of  failures  shows  that  fewer  towers 
have  failed  as  compared   with  the  collapse  of  stand-pipes. 

While  this  is  true,  it  is  also  a  fact  that  in  the  United  States 
there  are  very  many  more  stand-pipes  in  existence  than  towers 
and  tanks,  but  on  account  of  the  comparatively  small  increased 
cost  of  securing  a  greater  area  of  bearing  surface  for  the  support 
of  the  structure,  and  also  from  the  fact  that  by  the  wide  spread 
of  the  supporting  columns  of  a  tower,  the  stability  of  the  structure 
can  be  so  increased  that  the  resultant  of  the  overturning  moment 
of  the  wind  and  the  moment  of  the  weights  falls  well  within  the 
figure  limited  by  the  spread  of  the  columns,  where  the  same 
resultant  could  only  be  secured  for  a  stand-pipe  by  an  abnormal 
area  of  base. 

The  local  character  of  the  bearing  soil  exerts  a  considerable 
influence  upon  the  selection  of  either  type  of  structure,  and  this 
factor  should  be  carefully  considered  in  connection  with  the  dis- 
cussion of  foundations,  as  explained  in  the  succeeding  chapter. 

If,  after  a  careful  consideration  of  the  conditions  from  both 
an  engineering  and  a  financial  standpoint,  it  be  determined  that  a 
tower-and-tank  type  of  reservoir  is  preferable,  the  dimensions 
of  the  tank  being  assumed  from  reasoning  analogous  to  that  given 
in  considering  the  factors  in  stand-pipe  design,  a  strain-sheet 
is  prepared  as  explained  in  the  preceding  chapter,  but  which 
will  necessarily  be  modified,  as  will  be  explained  hereafter,  as 
far  as  the  thickness  of  the  lower  ring  and  bottom  plates  are  con- 
cerned; the  conditions  for  their  determination  being  changed. 

In  small  railway  water-supply  tanks  flat  or  horizontal  bottoms 
are  usually  provided,  supported  upon  wooden  sills  or  I  beams 
of  iron  or  steel,  attached  to  the  upper  deck  of  the  supporting 
structure.  In  such  cases  the  thickness  of  the  lower  ring  is  that 
determined  by  the  formula,  but  the  thickness  of  the  bottom 
plate  will  depend  upon  the  spacing  of  the  beams  or  sills. 

In  cities  or  towns  where  the  tower  and  tank  is  to  be  erected 
for  public  supply  some  other  form  of  bottom  is  generally  specified, 


D  E  SIGN  ING.  1 79 

for  the  reason  that  other  forms  require  somewhat  less  material; 
it  is  easier  to  secure  and  maintain  water-tight  joints;  all  parts 
of  the  bottom  are  accessible,  making  subsequent  and  necessary 
painting  possible;  the  stresses  are  less  than  in  the  flat  bottom; 
the  conical,  hemispherical,  or  compound- shaped  bottom  is  more 
symmetrical  and  pleasing  to  the  eye;  and,  last,  the  action  of  the 
effluent  exerts  an  automatic  scour  or  self-cleaning  effect  upon 
the  bottom  plates,  preventing  sedimentary  deposits,  which  are 
sufficient,  as  has  been  shown  in  the  discussion  of  flat-bottomed 
stand-pipes,  to  make  it  necessary  to  provide  some  form  of  man- 
head  permitting  ingress  for  removal  of  the  deposit  at  intervals. 
For  these  reasons  the  subsequent  discussion  of  suitable  bottoms 
will  be  limited  to  this  type. 

Fairhaven  Failure. — Since  the  complete  and  disastrous  failure 
of  the  pretentious  and  costly  water-tower  at  Fairhaven,  Mass., 
brief  mention  of  which  has  been  made  in  a  previous  chapter, 
attention  has  been  particularly  drawn  to  the  proper  design  of 
tank  bottoms,  their  connections,  and  the  importance  of  the  con- 
tinuous girder  construction.  Shortly  after  this  failure  numerous 
articles  were  contributed  to  the  technical  press,  the  most  logical 
of  which  is  that  prepared  by  Prof.  A.  Marston,  Civil  Engineering 
Department,  Iowa  State  College,  and  published  in  the  Engineer- 
ing News,  Dec.,  1901,  as  follows: 

"  I  have  been  very  much  interested  in  the  account  of  the  Fair- 
haven  water-tank  failure  published  in  your  issue  of  November  21. 
I  desire  to  call  your  attention  to  some  features  of  the  original 
design  and  of  the  modifications  of  that  design  made  during  con- 
struction which  were  not  mentioned  in  your  account  of  the  failure, 
and  which,  it  seems  to  me,  whether  they  did  or  did  not  actually 
cause  the  failure,  may  readily  have  done  so.  In  what  I  shall 
say  I  do  not  desire  to  be  put  in  the  position  of  in  any  way  criticis- 
ing the  engineer  who  prepared  the  original  designs.  The  Fair- 
haven  water-tower  was  a  pioneer  structure  of  its  kind.  In  most 
engineering  designs  some  features  cannot  be  calculated  and 


i8o 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 


-Ji'PL 


must  be  designed  in  accordance  with  the  results  of  experience. 
In  the  case  of  the  Fairhaven  tower  experience  to  point  out  features 
requiring  special  attention  in  the  design  was  lacking.  Again, 
very  serious  changes  (see  Engineering  News,  Nov.  21,  1901) 
from  the  original  design  were  made  in  the  construction  of  the 
tower,  and  I  consider  that  these  added  greatly  to  the  danger 
of  failure.  The  engineer  who  designed  the  structure  cannot  be 
held  responsible  for  its  failure,  in  my  opinion. 

"  In  Fig.  49 1  have  reproduced  your  sketch  (with  some  additions) 
showing  the  methods  of  supporting  the  tank  at  the  tops  of  the 

posts.  Owing  to  the  posts  having  a 
batter,  the  post  thrust  against  the 
bottom  of  the  circular  girder  will  have 
an  inward  horizontal  radial  com- 
ponent. From  the  original  descrip- 
tion of  the  tower  published  in  Engi- 
neering News  of  Sept.  5,  1895,  I 
judge  that  the  batter  was  about  i  to  8. 
With  the  tank  full  the  horizontal 
radial  component  would,  therefore, 
be  about  36,000  Ibs.,  as  indicated  in 
Fig.  49.  No  special  provision  appears 
to  have  been  made  in  the  design  to 
take  care  of  these  radial  pressures, 
except  as  the  lower  flange  of  the 
circular  girder  may  be  capable  of 

//  withstanding    them.     In    all    designs 

/  for  water-towers  these  forces  should  be 

provided  for,  and  usually  are  provided 
for  by  the  use  of  a  circular  girder  with 

its  web  horizontal.  The  company  which  builds  more  such 
structures  than  any  other  in  the  country  uses  solid-plate  webs. 
The  writer  is  accustomed  to  use  a  web  system  for  this  circular 
girder  composed  of  angles.  Usually  this  girder  is  utilized  to 


DESIGNING.  l8l 

form  the  floor  of  the  balcony,  which  I  consider  a  very  important 
feature  of  water-tower  designs,  as  it  enables  convenient  and 
careful  inspection  to  be  made  of  the  portion  of  the  tank  which 
is  most  liable  to  failure,  namely,  the  junction  of  the  tank  with 
the  supporting  posts.  In  the  case  of  the  Fairhaven  tank,  if  we 
consider  the  horizontal  radial  components  of  the  post  thrusts 
to  be  carried  only  by  the  lower  flange  of  the  circular  girder,  and 
if  this  lower  flange  had  been  made  continuous  past  the  posts, 
a  bending  moment  of  331,000  inch-pounds  and  a  thrust  in  the 
line  of  the  flange  of  67,000  Ibs.  would  result  immediately  over 
•each  post.  Counting  the  lower  flange  as  composed  of  two  3^X 
3iXj-in.  angles,  and  one  8X-J-in.  cover-plate  (see  Engineering 
News,  Sept.  5,  1895),  and  also  counting  in  3^  ins.  of  the  f-in. 
web  plate  of  the  circular  girder,  the  resulting  stress  on  the  outer 
fibre  would  be  38,400  Ibs.  compression  at  the  post  connection. 
As  built,  the  lower  flange  seems  not  to  have  been  continuous, 
and  this  bending  moment  would  have  to  be  carried  by  the  rivets 
of  the  connection  between  the  segments  of  the  circular  girder 
with  each  other  and  with  the  top  of  the  posts.  No  data  of  the 
connection  have  been  published  which  would  enable  the  resulting 
stresses  upon  the  rivets  to  be  computed,  but  under  any  reasonable 
assumption  it  seems  probable  that  they  must  have  all  along 
been  stressed  nearly  to  the  breaking  point  whenever  the  tank 
was  entirely  full  of  water. 

"As  the  formulas  for  the  computation  of  the  stresses  given 
above  are  not  widely  published,  the  writer  here  gives  them,  credit- 
ing them  to  two  students  of  the  Civil  Engineering  Department 
of  Cornell  University  (Transactions  of  the  Association  of  Civil 
Engineers  of  Cornell  University,  1896.) 

"At  any  point  A  in  the  circular  hoop  shown  in  Fig.  50  let  the 
bending  moment  from  the  pair  of  radial  forces,  P,  be  called  M, 
the  thrust  T,  and  the  shear  J.  Then 


1 82 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 


FIG.  50. 


"  In  addition  to  the  above  critical  stresses  in  the  circular  girder, 
it  should  be  observed  that  if  this  girder  fulfils  the  purpose  for 
which  it  was  intended,  that  of  transferring 
the  weight  of  the  tank  to  the  posts,  it  will 
be  subjected  to  a  large  bending  moment 
immediately  over  the  posts,  of  such  nature 
as  to  cause  tension  in  the  upper  flange  and 
compression  in  the  lower  flange.  This 
compression  in  the  lower  flange  has  to  be 
added  to  the  stresses  already  given,  and  in 
addition  it  should  be  noted  that  each  seg- 
ment of  the  circular  girder  would  have  a 
tendency  to  rotate  inwards  at  the  top  of 
the  post  connection  owing  to  the  fact  that 
it  is  not  straight  between  posts.  Cer- 
tainly the  circular  girder  should  have  been  made  continuous  as 
provided  for  in  the  original  plans,  and  the  fact  that  it  was 
built  in  segments  renders  the  upper  flange  incapable  of  carrying 
the  tension  over  the  posts,  and  this  tension,  so  far  as  the  friction 
from  the  heavy  load  can  do  this,  would  be  transferred  to  the 
flanged  portion  of  the  conical  bottom,  tending  to  disrupt  it  along 
a  radial  line. 

"  The  writer  does  not  consider  it  necessary  or  even  desirable 
to  use  a  circular  girder  under  the  sides  of  the  tank.  There  is 
no  way  of  preventing  the  tank  itself  from  acting  as  a  girder  to 
carry  the  loads  to  the  posts  if  we  desired,  and  the  writer  considers 
that  it  ought  to  be  strengthened  sufficiently  to  enable  it  to  do 
this  with  safety.  The  writer  would  not  put  any  manhole  in 
the  lower  ring  of  plates  of  the  tank. 

"In  the  case  of  the  Fairhaven  tank,  the.  lowest  side  ring  of 
plates  appears  to  have  been  made  of  just  about  the  thickness 
that  good  practice  would  require  for  a  stand-pipe  of  diameter 
and  height  equal  to  the  tank  above  this  point.  Now,  the  conical 
bottom  at  its  junction  with  the  sides  of  the  tank  is  subjected  to 


DESIGNING.  183 

bursting  stresses  greater  than  those^  in  the  sides  of  the  tank  in 
the  ratio  -; — ^,  where  0  is  the  angle  which  an  element  of  the 

cone  makes  with  a  horizontal  line.  I  am  unable  to  tell  exactly 
what  6  was  in  the  case  of  the  Fairhaven  tank  from  any  published 
data,  but  presume  that  it  was  in  the  neighborhood  of  45°.  If  6 
equals  45°,  the  upper  ring  of  plates  in  the  conical  bottom  was 
overstressed  about  40%  beyond  what  good  practice  would 
indicate  as  reliable.  In  addition  comes  the  stress  over  each  post 
due  to  the  fact  that  the  circular  girder  was  made  in  segments 
instead  of  continuous. 

"  Under  the  circumstances  indicated  above  the  writer  does 
not  consider  the  failure  of  the  tank  a  matter  for  surprise.  It 
may  readily  have  happened  that  the  lower  flange  of  the  circular 
girder,  after  having  been  repeatedly  stressed  beyond  the  elastic 
limit,  may  have  bent  inward  at  some  post.  The  result  would  be 
a  redistribution  of  the  stress  which  would  be  pretty  sure  to  tear 
the  tank  at  its  weakest  point,  which  in  this  case  was  the  conical 
bottom.  The  first  indication  of  failure  visible  from  the  ground 
would  be  a  stream  of  water  escaping  from  this  tear,  which  would 
be  immediately  followed  by  the  collapse  of  the  structure.  The 
writer  considers  this  the  most  probable  way  in  which  the  failure 
occurred,  but  if  for  some  unknown  reason  the  bottom  disrupted 
first,  the  fact  that  the  circular  girder  was  in  unstable  equilibrium, 
so  to  speak,  would  lead  to  the  immediate  collapse  of  the  structure. 
The  writer  considers  that  the  lessons  to  be  drawn  from  the  failure 
are  that  in  the  design  of  elevated  steel  tanks: 

"  i.  A  larger  factor  of  safety  should  be  used  for  the  curved 
bottom  than  for  the  vertical  sides  of  the  tank. 

"  2.  The  lower  portions  of  the  vertical  sides  of  the  tank  should 
be  strengthened  to  resist  the  shearing  and  other  girder  stresses 
caused  in  them  by  transferring  the  load  to  the  posts. 

"3.  The  junction  of  the  bottom  and  sides  of  the  tank  should 
be  held  true  tc  shape  and  the  radial  components  of  the  post 


184  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

thrusts  should  be  provided^ for  by  a  circular  girder  extending 
entirely  around  the  tank  and  having  its  web  system  horizontal. 

"  4.  A  balcony  should  be  provided  at  the  junction  of  the  bottom 
and  sides  of  the  tank,  to  permit  ready  inspection  of  this  most 
important  part  of  the  structure. 

"  The  writer  will  add  that  it  is  very  important  that  the 
loads  should  bear  centrally  on  th£  posts,  or  that  the  stresses  due 
to  eccentricity  of  loading  should  be  amply  provided  for." 

Consideration  of  Tank  Bottom  and  Connections. — During 
the  prolonged  discussion  of  the  Fairhaven  failure  Prof.  A.  Mars- 
ton  again  contributed  a  short  article  with  details  of  a  full  hemi- 
spherical tank  bottom  and  connections,  which  was  published  in 
the  Engineering  News  of  January,  1902,  and  this  design  is  re- 
produced here  as  Fig.  51. 

In  the  article  alluded  to,  Prof.  Marston  expresses  his  decided 
preference  for  this  type  rather  than  either  the  segmental  or  conical 
bottom,  urging  that  the  latter  introduces  a  radial  inward  pull 
on  the  joint,  liable  to  cause  trouble.  It  was  also  pointed  out 
that  the  stresses  in  a  hemispherical  bottom  are  only  one-half, 
while  those  developed  in  the  conical  bottom  are  larger  than 
those  in  the  vertical'  sides  of  the  tank;  therefore,  by  using  for  the 
bottom  the  same  thickness  of  plate  as  theoretically  determined 
for  the  shell,  the  hemispherical  bottom  would  develop  a  factor 
of  safety  twice  that  provided  for  the  vertical  sides. 

In  the  consideration  of  this  type  entirely  in  its  commercial 
and  practical  aspect,  an  expression  was  asked  of  a  representative 
of  one  of  the  great  bridge  companies,  himself  an  expert  in  the 
design  and  construction  of  such  structures,  and  who  replied  in 
part  as  follows:  "The  objection  to  the  hemispherical  bottom 
from  the  manufacturer's  point  of  view  is  not  nearly  so  strong  as 
it  was  a  few  years  ago,  and  there  is  now  no  difficulty  in  getting 
competitive  bids  on  the  manufacture  of  the  spherical  bottom. 
The  additional  costs  of  labor  required  for  manufacturing  spherical 
bottoms  are  usually  more  than  offset  by  the  saving  of  material 


DESIGNING.  185 

and  freight.  It  seems  to  me  good  policy  to  advocate  that  form 
of  bottom  which  gives  definite  stresses,  even  though  that  form 
of  construction  may  cost  more  in  some  cases. 

"  The  plates  of  the  spherical  bottom  should  be  made  about  1/16 
of  an  inch  thicker  than  the  figured  thickness,  to  make  allowance 
for  the  stretching  of  the  plates  in  shaping  them  and  to  give  pro- 
tection against  masses  of  falling  ice. 

"  Similarly  the  connection  of  the  bottom  to  the  cylinder  should 
be  made  stronger  than  the  figured  stresses  required. 

"  Whether  the  conical  or  hemispherical  bottom  is  used,  I  would 
prefer  to  connect  same  to  the  bottom  of  the  tank  cylinder  so 
that  the  metal  forming  the  joint  is  a  part  of  the  bottom  of  the 
circular  girder. 

"  The  post  connection  is  not  so  easy  to  make,  but  it  can  be 
satisfactorily  solved.  The  design  for  the  water-tower  for  the 
Iowa  State  College,  at  Ames,  Iowa,  published  in  recent  editions 
of  Johnson's  '  Framed  Structures '  gives  a  satisfactory  solution 
of  this  connection.  This  structure  was  designed  by  Prof.  A.. 
Marston  (Figs.  51-52). 

The  detail  which  shows  the  posts  riveted  direct  to  the  tank 
shell  has  proved  very  satisfactory,  as  it  gives  a  rigid  connection. 
However,  care  must  be  taken  that  the  centre  of  gravity  of  the 
connection  falls  on  the  axis  of  the  column.  Theoretically  the 
curved  girder  in  the  horizontal  plane  which  resists  the  horizontal 
thrust  at  the  top  of  the  posts  should  be  at  this  centre  of  gravity. 
Practically  it  is  more  convenient  to  place  it  on  a  level  with  the 
junction  of  the  bottom  and  cylinder.  This  arrangement  produces 
some  bending  stresses  in  the  post  and  its  connections,  but  ordi- 
narily they  will  not  be  serious." 

In  bottoms  and  connections  of  this  type  especial  care  should 
be  taken  in  the  matter  of  "laying  out"  and  shop- work,  and  it. 
has  been  suggested  that  for  the  joint  between  the  sides  and  bottom 
the  pieces  should  be  assembled  at  the  shop  and  rivet-holes  reamed 
through;  also  that  adjacent  pieces  of  the  bottom  should  be  fastened 


186 


TOWERS  AND    TANKS  FOR    WATER-WORKS 


together  in  the  shop  and  those  of  one  piece  marked  from  the  holes 
of  the  other. 


t .v 


Balcony  Laid  with 
If  "Oak  Floor,  Fastened 
to  Nailing  Strips, 
Bolted  tc  6"Ls.      E~ 


gtiff.L 


SECTIONAL  PLAN 

C-D 

FIG.  51. 

No  heating  or  excessive  hammering  is  necessary  or  should 
t>e  permitted.     The  bottom  and  connection  as  shown  in  Prof. 


DESIGNING. 


I87 


Marston's  design  are  not  novel  in  their  general  character,  as 
this  type  has  been  used  exclusively  as  a  specialty  of  a  large  Western 
bridge  and  structural  works,  which  has  erected  from  eighty 
to  one  hundred  water-towers  with  spherical  bottoms  for  towns, 
cities,  and  industrial  plants,  the  largest  being  a  tank  32  ft.  in 


Galv.FiniaU_4 
Washer^ 

'&        %         #         fi'/Vx  U'Circulan 
I..J      i      j      7      i       i  VStftfil  fiastino"^ 


-Wlock 


-L.6-X8TXI- 

-  Sheet  Metal  With  Washer 

Strap  Iron  Brackets 
every  a'ft. 

FIG.  52. 

diameter,  and  with  a  shell,  exclusive  of  full  hemispherical  bottom, 
40  ft.  high.  The  capacity  of  this  tank  is  300,000  gallons. 

Prior  to  the  Fairhaven  failure,  the  Jacksonville,  Florida, 
water-tower  had  been  constructed,  brief  mention  of  which  has 
been  previously  made.  As  stated,  this  tank  was  30  feet  in  diam- 
eter and  45  feet  high,  with  conical  bottom  and  connections  as 
shown  in  Fig.  i. 

In  its  general  appearance  this  tower  was  very  similar  to  that 
at  Fairhaven  (Fig.  3),  although  differing  in  its  design  for  bot- 
tom connections  and  other  structural  details. 

The  simple  post  connections  of  the  Jacksonville  type,  as  well 
as  the  ease  in  laying  out  and  assembly,  have  made  this  a  most 


1 88  TOWERS  AND    TANKS  FOR  WATER-WORKS. 

popular  form  for  manufacturers,  and  it  is  undoubtedly  true  that 
for  these  reasons  closer  figures  have  been  obtained  and  broader 
competition  secured  when  this  class  of  bottom  and  connections 
have  been  specified.  In  the  recent  past  nearly  all  of  the  smaller 
water-works  tanks  have  had  the  conical  bottom  except  those 
designed  and  erected  by  the  structural  works  making  a  specialty 
of  the  spherical  type  as  hereinbefore  mentioned.  To  offset 
its  advantages,  it  has  other  faults  beside  those  of  indeterminate 
stresses,  and  necessity  for  heating  and  flanging  its  segments, 
principally  structural  reasons,  as,  for  instance  the  difficulty  in 
driving  a  few  of  the  rivets  in  the  radial  seams  of  the  bottom  and 
the  vertical  seams  of  the  cylinder;  besides  there  is  a  difficulty 
in  painting  in  the  angle  between  the  bottom  and  the  cylinder. 
The  first  coat  would  probably  be  properly  applied,  but  this  in- 
accessible and  out-of-the-way  recess  would  very  likely  be  sub- 
sequently neglected,  exposing  this  vital  point  of  the  structure  to 
corrosion. 

Notwithstanding  these  facts,  with  the  exception  of  the  Fair- 
haven  tank,  which  is  hardly  a  satisfactory  type,  no  failures 
have  to  this  time  been  reported,  and  such  towers  have  generally 
proved  entirely  satisfactory.  In  one  of  his  own  designs  (Fig.  53) 
the  author  has  combined  the  two  types,  using  a  spherical  segment 
for  the  section  of  the  bottom  intended  to  be  riveted  to  the  tank, 
which  segment  is  tangent  to  a  cone-shaped  lower  section,  termi- 
nating at  the  orifice. 

The  Circular  Girder. — In  the  theoretical  discussion  of  the 
circular  girder  it  \vas  showTi  that  the  stresses  produced  were  a 
vertical  shear,  a  torsion  moment,  and  bending  moments  between 
and  over  points  of  support.  Since  the  maximum  stress  is  the 
bending  moment  over  the  point  of  support,  in  the  consideration 
of  the  girder,  the  shear  and  torsion  stresses  are  not  generally  of 
prime  importance,  although  all  of  the  stresses  produced  should 
be  given  attention.  These  stresses  have  been  analyzed  and 
tabulated  for  girders  having  from  four  to  twelve  points  of 


DESIGNING.  1 89 

support,  and  are  included  in  the  chapter  "  Stresses  in  a  Steel 
Water-tower." 

On  account  of  the  maximum  stress  and  heavy  bending  moment 
over  each  point  of  support,  it  cannot  be  too  strongly  insisted 
upon  that  prudence  demands  provision  for  a  continuous  curved 
girder.  While  it  is  true  that  a  number  of  water-towers  have 
been  built  without  the  use  of  the  circular  girder  other  than  the 
tank  cylinder  itself,  the  only  provision  being  an  increase  in  the 
thickness  of  the  lower  tank  ring  over  that  required  for  hydrostatic 
stresses,  such  practice  is  likely  to  cause  trouble,  and  a  girder 
should  be  designed  with  a  web  consisting  of  the  lower  plate 
slightly  heavier  than  theoretically  determined  as  necessary,  and 
reenforced  with  angle  stiffeners,  and  provided  with  both  bottom 
and  top  flanges.  In  discussing  the  riveted  girder,  Carnegie's 
Handbook  has  this  to  say:  "The  web  of  the  girder  must  be 
made  of  such  thickness  that  there  will  be  no  tendency  to  buckle 
and  that  the  vertical  shearing  stress  per  square  inch  will  not 
exceed  10,000  pounds. 

"  This  shearing  stress  is  greatest  near  the  supports  and  is 
obtained  by  dividing  half  the  load  upon  the  girder  (providing  the 
load  is  symmetrically  applied)  by  the  web  section.  The  first 
condition  (security  against  buckling)  is  attained  when  this  shear- 
ing stress  does  not  exceed 

1 1 ,000 


# 


in  which  d  represents  the  depth  of  web  in  clear  of   flange  of 
girder,  and  /  the  thickness  of  one  web  plate  in  inches. 

"  Ordinarily  this  formula  gives  a  lower  stress  than  10,000 
pounds,  so  that  both  conditions  are  usually  attained  when  the 
first  is.  Instead  of  increasing  the  thickness  of  the  web,  it  may  be 
stiffened  by  means  of  vertical  angles  riveted  to  it  at  proper  inter- 


TOWERS  AND    TANKS  fOR    WATER-WORKS. 

vals.  These  latter  should  always  be  less  than  the  depth  of  the 
girder.  .  .  .  Stiffeners  should  always  be  used  at  or  near  the  sup- 
ports, and  at  any  point  where  there  is  a  concentration  of  heavy 
loads. 

"  The  duty  of  these  stiffeners  in  such  cases  is  twofold:  first, 
to  prevent  buckling  of  the  web;  second,  to  transmit  the  shear 
to  the  web  by  means  of  abutting  areas  and  the  rivets,  both  of 
which  must  be  sufficient  for  the  purpose." 

There  has  not  to  this  time  been  formulated  any  rational 
theory  for  either  the  spacing  or  size  of  stiffeners  in  plate 
girders,  although  it  has  erroneously  been  assumed  that  when 
stiffeners  are  introduced  at  intervals  not  exceeding  the  depth 
of  the  girder,  the  conditions  are  analogous  to  those  of  a 
truss  composed  of  posts  and  tension  members  and  to  the 
solution  of  which  the  Gordon  or  other  compression  formula 
might  be  applied.  As  a  matter  of  fact,  both  size  and  spacing 
of  vertical  stiffeners  are  largely  matters  of  judgment  and  are 
governed  by  the  usual  practice  for  particular  cases.  Allowable 
flange  strains  are  usually  taken  as  15,0x30  pounds.  The  rivets 
generally  used  are  f-inch,  spaced  not  more  than  6  inches  and 
closer  than  this  for  heavy  flanges.  Where  loads  are  great,  es- 
pecial calculation  for  rivet-spacing  should  be  made,  allowing 
9000  pounds  per  square  inch  for  shearing  and  18,000  pounds 
per  square  inch  for  bearing.  The  unsupported  width  of  flange- 
plates  subject  to  compression  should  not  exceed  32  times  their 
thickness,  nor  should  the  flange-plates  extend  beyond  the  outer 
line  of  rivets  more  than  5  inches  nor  more  than  8  times  their 
thickness.  The  term  "flange"  as  applied  to  riveted  girders 
embraces  all  the  metal  in  top  or  bottom  of  girder  exclusive  of 
web  plate;  or  in  the  case  of  a  rolled  beam  or  channel  with  top 
and  bottom  plates,  all  metal  exclusive  of  that  part  of  the  web 
between  fillets.  With  a  circular  girder  as  with  a  simple  beam, 
its  ability  to  support  a  load  depends  upon  the  strength  and  ar- 
rangement of  its  fibres,  limited  by  the  distance  between  supports. 


DESIGNING.  IQI 

Since  the  width  of  the  girder  is  small  compared  with  its  radius, 
the  solution  of  the  stresses  in  a  circular  hoop  may  be  applied, 
and  the  girder  designed  to  resist  the  whole  weight  of  the  tank, 
including  its  own  weight  and  the  contents  of  the  tank;  a  radial 
inward  thrust  at  the  top  of  each  of  the  posts,  and  reactions  due 
to  wind  stress. 

In  the  riveted  plate  girder  it  is  usual  to  assume  that  the  flange 
sustains  the  horizontal  and  the  web  all  of  the  vertical  strains 
due  to  the  load,  the  flange  acting  under  tension  and  the  web 
being  subject  to  shear.  The  tank  plate  is  usually  taken  as  the 
web  of  the  curved  girder;  angles  are  riveted  to  the  web  as  flanges, 
and  stiffeners  are  introduced  at  proper  intervals  consisting 
of  one  or  more  angles  or  channel  shapes.  Such  a  continuous 
girder,  when  properly  proportioned,  provides  an  economical 
and  effective  support  for  the  gravity  and  wind  stresses  to  which 
the  tank  is  subject.  To  determine  the  safe  load  for  the  girder, 
its  elements  must  first  be  found. 

The  principles  of  moments  are  applicable  to  areas  as  well  as 
to  weights,  and  from  such  application  an  equation  is  obtained 
from  which  the  value  of  c,  or  the  distance  from  the  neutral  axis, 
passing  through  the  centre  of  gravity  of  the  shape  to  the  most 
remote  fibres  can  be  determined. 

If  a  be  any  area  and  z  the  distance  from  its  centre  of  gravity 
from  an  axis,  the  product,  az,  is  called  the  static  moment  of  the 
area.  The  sum  of  the  static  moments  of  all  parts  of  the  figure 
is  represented  by  2az,  and  if  A  be  the  total  section  area,  then 

laz 

C=  7—. 


Since  the  moment  of  inertia  of  a  plane  surface  with  respect  to  an 
axis  is  the  sum  of  the  products  obtained  by  multiplying  each 
elementary  area  by  the  square  of  its  distance  from  the  neutral 
axis,  the  elementary  areas  of  the  compound  shape  and  the  dis- 


192  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

tance  c  having  been  determined,  their  summation  is  the  moment 
of  inertia  /,  of  the  shape,  and  the  moment  of  resistance  Rt  of 

the  girder,  is  -. 
c 


SUPPORTING   TOWER. 

For  small  tanks  with  capacities  of  from  20,000  to  30,000 
gallons,  possibly  a  three-post  tower  is  the  most  convenient  and 
economical  type,  and  for  such  small  structures  presents  a  neat 
and  trim  appearance. 

Larger  tanks  should  be  built  of  four,  six,  and  eight  columns, 
but  for  capacities  of  from  30,000  to  90,000  gallons  possibly  the 
four-post  tower  is  more  satisfactory  on  account  of  the  material 
saved  in  the  design  because  the  compression  members  are  of 
larger  and  more  convenient  dimensions  than  where  the  load  is 
distributed  amongst  a  greater  number  of  supporting  points. 

The  increase  in  the  number  of  supports  does  not  indicate  a 
corresponding  security  and  strength,  but  unquestionably  espe- 
cially tall  towers  and  capacious  tanks  equipped  with  more  than 
four  legs  produces  a  decidedly  more  stable  as  well  as  symmetrical 
appearance  than  the  four-post  variety,  and  in  such  cases,  the 
loads  will  be  large  enough  to  require  sections  of  economical 
dimensions. 

Where  a  hemispherical-bottomed  tank  is  specified  and  to  be 
riveted  directly  to  the  columns,  increasing  the  points  of  support 
allows  a  better  distribution  of  the  loads,  and  the  likelihood  of 
unequal  loading  is  thereby  minimized. 

A  majority  of  the  towers  are  built  with  posts  slightly  in- 
clined, and  without  change  of  inclination  fiom  the  top  to  the 
base,  although  a  few  towers  have  been  constructed  with  vertical 
legs,  and  of  late  several  have  been  designed  with  change  of 
inclination  in  the  batter  posts  at  panel-points,  producing  a 
pleasing  curve  in  the  tower  outline. 


DESIGNING.  193 

In  the  latter  case  column  sections  are  straight  between  panel- 
points,  these  being  located  upon  the  arc  of  a  circle  or  at  points 
of  a  parabolic  curve,  according  to  the  fancy  of  the  designer. 
Straight  posts  are  somewhat  cheaper,  but  the  additional  cost 
of  the  curved  outline  may  be  warranted  on  account  of  the  im- 
proved appearance  and  more  graceful  lines. 

Several  years  since  column  sections  and  formulas  of  structural 
engineering  underwent  careful  investigation  and  analysis.  This 
sharp  rivalry  for  supremacy  has  produced  its  natural  result, 
the  survival  of  the  fittest,  until  to-day  all  column  sections  are 
practically  eliminated  that  fail  to  include  standard  elements, 
as  I  beams,  angles,  channels,  and  plates,  and  the  standard- built 
column  of  to-day  consists  of  angles  latticed,  angles  and  plates, 
and  the  latticed  double  channel,  formed  either  of  plates  and 
angles  cr  the  latticed  double-channel  column. 

The  seeming  exception  to  this  rule  is  the  Z-bar  column,  but 
as  with  the  other  discarded  column  sections,  its  popularity  seems 
somewhat  on  the  wane  judging  from  the  following  expression 
of  an  experienced  structural  engineer:  "These  columns  are 
excellent  from  a  structural  point  of  view,  but  are  somewhat  more 
difficult  to  use  where  bevelled  connections  are  required.  Further- 
more, Zee-bar  columns  seem  to  be  going  out  of  use;  just  why  I 
do  not  know,  but  at  the  present  time  the  demand  for  Zee  bars 
is  comparatively  light,  and  the  result  is  that  the  mills  do  not 
roll  them  very  often,  and  there  are  likely  to  be  serious  delays 
occasioned  on  work  where  Zee  bars  are  specified.  The  quantity 
of  Zee  bars  required  for  a  water-tower  is  not  sufficient  to  warrant 
a  special  rolling.  In  one  case  last  year  we  were  delayed  three 
or  four  months  for  this  reason.  If  the  Zee-bar  shape  is  specified 
for  any  reason,  it  can  be  built  of  an  I  beam  and  two  channels. 
Laced-channel  columns  are  very  satisfactory,  especially  so  for 
the  rigid  connection  at  the  top  referred  to  above.  As  all  sizes 
of  channels  are  used  in  large  quantities,  there  is  usually  no  dif- 
ficulty in  procuring  them  within  any  reasonable  time." 


i94 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 


The  tendency  toward  standardizing  is  undoubtedly  account- 
able for  the  facts  presented. 

In  designing  a  girder  capable  of  safely  carrying  all  the  im- 
posed stresses,  a  reduction  of  the  length  of  span  and  consequent 
decrease  of  the  size  and  weight  of  the  members  of  the  circular 
girder  may  be  accomplished  by  increasing  the  number  of  sup- 
porting columns;  or  the  length  of  span  may  be  reduced  by  de- 
signing short  diagonal  struts,  usually  two  for  each  column, 
reducing  the  length  of  span  in  accordance  with  the  number  of 


\ 


H 


FIG.  53. 

struts  supplied,  two  such  struts  to  each  column  of  a  four-column 
tower  giving  twelve  bearing  points  instead  of  four  along  the 
curved  girder;  but  this  method  of  reducing  the  length  of  un- 
supported span  is  open  to  objection  on  account  of  the  eccen- 
tricity of  loading  and  the  multiplication  of  members  and  joints. 
The  usual  four-,  six-,  and  eight- column  towers  being  made 
up  of  certain  standard  shapes,  is  laid  out  and  riveted  together 
at  the  shop,  and  the  lengths  so  constructed  are  carefully  marked, 


DE-SIGNING.  195 

to  be  afterwards  readily  assembled  in  the  field,  and  at  which 
time  only  the  riveting  at  the  junction-  or  panel-points  is  neces- 
sary. 

At  this  time  the  two  favorite  types  are  undoubtedly  the  Z  bar 
and  the  double-channel  latticed  column,  both  possessing  in- 
dividual advantages  for  structural  purposes. 

Where  the  double  channel  is  used,  it  should  be  so  latticed 
as  to  prevent  individual  weakness  and  that  all  parts  should  act 
as  a  unit  in  the  combined  section.  That  there  may  not  be  a 
tendency  in  the  channels  to  bend  between  the  points  of  bracing, 
the  distance  /  (Fig.  53)  should  be  made  to  equal  the  total  length 
of  strut  multiplied  by  the  least  radius  of  gyration  of  a  single 
channel  and  the  product  divided  by  the  least  radius  of  gyration 

of  the  whole  section,  or  /  =  -JT, 

K 

where  /  =  length  between  bracing; 
L  =  total  length  of  strut; 

r  =  least  radius  of  gyration  of  a  single  channel; 
R  =  least  radius  of  gyration  of  the  whole  section. 

In  practice  the  distance  /  is  taken  considerably  less,  the  dis- 
tance as  determined  by  the  formula  being  more  or  less  used  as  a 
guide. 

The  Z-bar  column,  consisting  of  four  "Z "-shaped  bars  riveted 
to  a  web  plate  possesses  so  many  structural  advantages  that  for 
building  purposes  it  has  had  a  wide  popularity  and  extensive 
use,  and  whether  the  tendency  toward  standardization  will 
render  it  obsolete  remains  to  be  seen,  although  this  would  seem 
the  case. 

In  lengths  ranging  from  64  to  88  radii,  from  careful  test, 
an  average  ultimate  resistance  of  35,650  pounds  was  determined 
for  iron  columns,  and  an  assumption  that  steel  bars  will  have 
some  20%  higher  value.  Their  great  adaptability  for  making 
connections  with  other  columns  and  members,  their  accessibility 
for  inspection,  painting,  and  repair,  the  small  number  of  rivets 


196  TOWERS  AND    TANA'S  FOR    WATER-WORKS. 

required  for  connection,  make  this  a  most  excellent  section  for 
supporting  columns  of  a  water-tower. 

Six-inch  columns  are  manufactured  from  12  to  30  feet  long; 
8-inch  are  from  1 8  to  40  feet  in  length,  and  12-,  14-,  16-,  18-,  and 
2O-inch  columns  are  made  as  long  as  50  feet.  In  the  tower  design, 
where  junctions  are  made  between  lengths,  horizontal  struts  are 
introduced  between  columns,  and  are  sometimes  inserted  radially, 
the  latter  rather  for  the  purpose  of  stiffening  the  tower  than 
calculated  as  of  theoretical  value  in  transmitting  stresses.  There 
is  also  usually  inserted  at  the  foot  of  the  tower  a  strut  or  tie. 
When  this  is  omitted,  as  is  sometimes  the  case,  the  foundation 
loads  are  not  vertical,  there  being  a  horizontal  component.  This 
point  should  be  taken  into  consideration  in  the  design  of  the 
foundations,  making  the  resultant  of  the  loads  on  the  foundation 
come  in  the  centre  of  the  bearing  surface  and  thus  avoid  the 
liability  of  unequal  settlement. 

Horizontal  members  of  the  tower  are  subject  to  similar  stress 
as  the  vertical  columns,  but  it  is  to  be  noted  that  in  particularly 
long  lengths,  the  weight  of  the  strut  itself  produces  deflections 
that  should  be  given  consideration. 

In  water-tower  design,  such  horizontal  struts  are  generally 
formed  of  four  angles  back  to  back,  and  riveted  either  to  a  central 
web  plate  or  to  lattice  bars,  but  where  the  span  and  load  is  con- 
siderable, the  double-latticed  channels  are  preferable. 

Columns  and  struts  generally  fail  under  the  stress  produced 
by  combined  compression  and  bending. 

The  investigation  of  a  column  under  a  given  load  consists 
in  computing  the  unit  stress  from  formulas  and  then  comparing 
this  with  the  ultimate  strength  and  elastic  limit  of  the  material, 
taking  into  consideration  such  conditions  as  the  effect  of  a  steady, 
variable,  or  sudden  load  with  further  reference  as  to  how  the 
column  ends  are  secured. 

When  the  length  of  the  column  and  load  to  be  carried  by  it 
is  given,  the  design  consists  in  selecting  suitable  materials  and 


DESIGNING. 


I97 


proportioning  the  section  so  that  the  unit  stress  will  be  proper 
and  reasonable.  On  page  105  column  formulas  are  discussed 
and  tables  are  given  for  the  investigation  and  design  of  columns 
and  struts,  while,  as  has  been  stated,  most  of  the  manufacturers' 
lists  furnish  correct  tabulation  of  the  elements  of  the  standard 
.shapes. 

GENERAL   DETAILS. 

Tank-cover. — Small  water-towers  are  generally  open  at  the 
top  and  are  provided  with  a  circumscribing  angle,  usually  sur- 
mounted by  a  malleable  iron  cresting  of  ornamental  design, 
but  with  tanks  of  capacities  as  large  as  say  50,000  gallons.  The 


10       !       ROOF  CONNECTIONS. 


FIG.  54. 


FIG.  55. 


practice  is  to  provide  some  sort  of  cover,  the  simplest,  and  prob- 
ably the  best,  being  a  light  steel-plate  roof,  projecting  over  the 
cylinder  and  terminating  with  a  light  circular  eaves-angle,  forming 
a  conical  cover.  This  design  may  be  elaborated  by  extending 
the  eaves-angle,  back  of  which  may  be  riveted  to  a  bent  plate 
a  steel  facia  plate  as  shown  in  Figs.  54-55,  or  omiting  the  lat- 


198  TOWERS   AND    TANKS  FOR    WATER-WORKS. 

ter,    a   galvanized  and  ornamental  cornice  may  be  introduced, 
riveted  to  the  eaves-angle  and  tank-plate  or  as  shown  in  Fig.  52. 

For  tanks  of  larger  capacities,  rafters  consisting  of  steel  angles 
or  channels  may  be  specified,  spaced  to  carry  a  light  steel  roof, 
or  provided  with  purlins  upon  which  is  laid  a  wooden  roof  covered 
with  galvanized  steel  plate.  Such  construction  permits  gables  and 
other  architectural  features.  In  the  design  of  the  Jacksonville, 
Fla.,  water-tower,  the  cone-shaped  roof  was  surmounted  by  four 
gables,  and  its  apex  was  adorned  by  an  elaborate  finial,  and  in 
which  was  introduced  an  electric-light  globe. 

With  curved  rafters  a  pagoda-shaped  roof  is  formed.  This 
design,  while  ornamental  in  detail,  is  probably  no  more  desirable 
than  the  conical  roof  either  in  construction  or  actual  appearance. 

For  ornamentation  as  well  as  to  stiffen  the  roof  construction, 
a  wooden  or  gas-pipe  flagstaff,  commencing  at  the  top  of  the  tank 
proper,  secured  by  radial  ties  to  its  shell  and  projecting  through 
a  bent  steel  collar  plate  at  the  roof  apex,  is  sometimes  added, 
otherwise  for  tanks  of  large  diameters  a  vertical  rod  and  radial 
ties  similar  to  those  shown  in  Fig.  52  should  be  required. 

Trolley-rail. — Some  18  to  24  inches  below  the  circumscribing 
angle  or  plate  at  the  top  as  suitable  shape,  as  a  Z  bar,  should 
be  riveted  to  the  shell  to  form  a  rail  for  a  painter's  trolley  or  trav- 
eller, and  which  serves  the  dual  purpose  as  a  convenience  and 
a  stiffener  to  the  top  of  the  tank. 

Ladder. — If  the  posts  are  latticed,  the  lacing  may  be  used 
to  reach  the  girder  at  the  top,  otherwise  along  one  of  the  legs, 
commencing  about  ten  feet  from  the  ground,  a  light  ladder,  con- 
sisting of,  say,  two  2"Xf  bars,  connected  by  J"  horizontal  rungs, 
spaced  18  to  24  inches  should  be  fastened  at  intervals  of  about 
10  to  12  feet  with  steel  clips  to  the  post  and  leading  to  a  2o-inch 
opening  in  the  balcony  floor,  extending  along  the  tank  shell  and 
terminating  at  its  top.  When  roofed,  a  trap  opening  of  about 
20  inches  and  an  opening  in  the  roof  overhang  should  be  pro- 
vided. As  there  is  an  element  of  danger  in  the  opening  in  the 


DESIGNING. 


199 


balcony  floor,  it  is  sometimes  thought  desirable  to  carry  the 
ladder  from  the  top  of  the  post  over  the  gallery  rail  as  shown  in 
Fig.  56- 


h 


10'x  i'Splice  PI 


56'xfg-"  PLSi'de        I 
of  Tank  _ 


15"x  I' Splice  and 

Stiffener  PI. 
Directly  over  Web  f 
El.of  Column.        ) 


!  So  oo  o 

0 

0      0 

0   g 

o    o 

o0< 

0     >0 

o 

°<   ? 

o  ° 

o    o 

0  °< 

°(  ? 

o  c 

o    o 

O      ( 

°(    ° 

0   £ 

0 

o  c 

o 

° 

o 

° 

0   ° 

0 

0     i 

?  o 

o  ° 

Q 

°oc 

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0  010  0 

*•©  lo  cf 

6   6  010  o 
g   5  o|  o  o 

'/] 

|V 

\   f4|'x  |"x  26' Bearing 

\<|  and  Lateral  Rod 

I  Connection  Pi. 


FIG.  56. — Detail  of  Junction  Between  Sides  and  Bottom  of  Elevated  Steel  Tanks. 
(Designed  by  Prof.  A.  Marston.) 

In  cold  climates  where  masses  of  ice  may  form  inside  the 
tank,  the  rigid  inside  ladder  should  be  dispensed  with,  and  in 
such  cases  a  rope  ladder  may  be  used  when  required. 


200  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

Balcony. — The  necessity  for  a  circumscribing  balcony  has 
been  discussed  and  emphasized.  Its  design  permits  considerable 
latitude  in  the  ornamentation  of  brackets,  railing,  and  other 
details.  While  wooden  floors  are  frequently  used  as  shown  in 
Fig.  51  and  Fig.  56,  a  simpler  and  more  durable  floor  is  that 
made  of  segmental  steel  plate,  \  to  5/16  inch  thick,  with  drain 
holes  as  shown  in  details  of  Fig.  57.  Small  and  cheap  water- 
towers  generally  have  a  gas-pipe  post  and  balcony  rails,  but  the 
effect  is  poor  and  generally  unsatisfactory. 

Supply  Pipe. — Flanged  pipe  is  sometimes  specified  for  the 
supply  main,  but  the  ordinary  cast-iron  pipe  of  the  bell  and  spigot 
type  answers  every  purpose.  An  expansion  joint  should  be 
insisted  upon,  located  near  the  tank  connection.  Such  a  joint 
is  shown  in  Fig.  i.  In  full  hemispherical  bottoms,  the  lower 
plate  is  usually  formed  of  dished  steel  head,  and  at  its  lowest 
point  a  standard  expansion  joint  should  be  riveted. 

Where  the  vertical  inlet  pipe  enters  the  distributing  system, 
a  cast-iron  foot  elbow  should  be  provided,  with  flat  base  plate 
resting  upon  a  masonry  pedestal.  The  lower  part  of  the  pipe 
and  elbow  should  be  incased  in  a  circular  masonry  chamber  as 
a  protection  and  support  of  a  frost  case  where  this  is  necessary. 
Where  the  supply  pipe  is  comparatively  small,  a  water-gate 
should  be  inserted  at  a  convenient  height  above  ground  and 
provided  with  a  hand- wheel,  otherwise  the  valve  should  be  placed 
on  the  distributing  main  just  outside  of  the  foot  bend. 

Frost  Proofing. — In  icy  latitudes  the  supply  pipe  should  be 
protected  from  freezing  by  a  frost-case.  In  extremely  cold 
climates  the  tank  bottom  is  tapped  for  a  steam-pipe,  which  is 
led  inside  of  the  case,  but  ordinarily  this  detail  is  omitted,  and 
only  wooden  boxing  or  circular  laggings,  constructed  with  layers 
of  tar-paper  between  the  sections  of  lagging,  spaced  to  provide 
from  two  to  four  2-inch  air  spaces,  is  specified.  A  neater  and 
more  durable  construction  is  to  make  the  outer  casing  of  light 
steel  plate,  say  3/16  inch,  flanged  with  light  angles  and  bolted 


DESIGNING. 


201 


-    R=13V-          --> 
Lat.  Rail  _ 

*«•«•          ^"*3*>       J 
2^  I  i.i  713  I— *J  , 


CIRCULAR  GIRDER, 
BALCONY  AND  BRACKET.      |/<i«  °w«  H- 

JIL^'-^MiL     i  ,',„•. 


•i 

I 
**- 


H--A 


FIG.  57. 


202  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

in  sections  of  10  to  12  feet.  The  supply  pipe  should  be  secured 
in  every  tower  panel  by  a  metal  collar,  from  which  radial  rods 
should  lead  to  each  post.  Where  there  is  little  likelihood  of  frost, 
the  case  may  be  entirely  omitted  and  the  supply  pipe  supported 
simply  by  the  collar  or  band  and  the  steel  rods. 

Connections. — Since  nearly  all  of  the  large  steel  companies 
catalogue  and  keep  in  stock  Z-bar  columns  of  various  sizes,  in 
their  publications  they  also  give  designs  for  standard  connec- 
tions, including  capitals,  pedestals,  panel-point  and  end  con- 
nections, with  bills  of  material  and  calculated  reactions.  The 
Z-bar  column  can  be  so  placed  that  with  the  four-post  tower 
the  connections  are  square,  but  when  the  post  is  a  column  built 
•of  latticed  channels,  it  is  usual  to  connect  the  horizontal  struts 
by  bent  jaw  plates  riveted  to  the  column. 

The  connection  at  the  top  of  posts  consists  of  a  bearing  plate, 
reenforced  with  angles,  and  the  flange  of  the  circular  girder  is 
riveted  as  may  be  convenient  to  the  bearing  plate.  In  some 
designs  (Fig.  51)  the  bearing  plate  is  bent  and  forms  a  connection 
for  the  diagonal  rods.  The  pedestal  or  footing  is  generally  a 
steel  plate,  reenforced  also  with  angles,  but  often  a  cast-iron 
bearing  plate  or  shoe  is  designed.  The  thickness  of  these  base 
plates  depend  upon  the  superimposed  load  and  vary  from  \  inch 
to  if  inches.  The  other  dimensions  of  the  bearing  plate  at  the 
base  must  be  such  as  to  provide  sufficient  area  for  the  proper 
distribution  of  the  weight  over  the  masonry  foundations  and 
generally  assume  at  100  Ibs.  per  square  inch  of  surface  upon 
brick  masonry,  but  a  capstone  is  usually  specified.  The  load 
which  may  be  allowed  upon  monolithic  piers  varies  with  the 
texture  of  the  stone  and  ranges  from  15  to  30  tons  per  square 
foot.  This  matter  is  further  discussed  in  a  subsequent  chapter, 
and  in  which  the  question  of  anchorage  is  also  considered.  In 
the  ordinary  tower  the  connections  are  rigid,  but  in  the  design 
of  a  recently  constructed  water-tower  having  a  capacity  of  150,000 
gallons  and  a  vertical  height  of  tower  of  200  feet,  the  bottom  of 


DESIGNING.  203 

each  footing  had  an  imbedded  cast-iron  washer  30X12^  inches 
and  i  inch  thick,  with  a  horizontal  rib  6  inches  deep  and  i  inch 
thick  on  its  under  side.  Cylindrical  nut  seats  17^  inches  apart 
were  formed  in  the  rib  so  that  two  2|-inch  anchor  bolts  took 
bearing  at  the  bottom  of  the  rib  and  extended  through  it.  One 
pair  of  diagonally  opposite  posts  were  constructed  with  sliding 
seats  to  allow  for  temperature  movements,  while  the  other  two 
posts  were  bolted  rigidly  to  the  foundations. 

Wind-bracing. — The  effect  of  the  wind  upon  the  water-tower 
should  be  provided  for  by  adjustable  diagonals  secured  to  ad- 
jacent columns  or  horizontal  struts  near  their  junctions  with 
the  columns.  The  horizontal  component  of  this  stress  is  taken 
up  by  the  horizontal  struts,  while  the  vertical  component  of  the 
stress  is  taken  up  by  the  tower-posts,  and  these  latter  must  be 
added  to  the  loads  to  which  the  posts  are  subjected. 

These  diagonal  brace  rods  act  in  tension,  dependent  upon  the 
force  and  direction  of  the  wind,  each  alternate  set  of  rods  coming 
into  service  at  the  same  time.  After  erection,  the  tower  when 
subject  to  its  maximum  load  may  become  distorted  a  little  through 
settlement,  therefore  the  rods  should  be  made  in  two  sections 
and  provided  with  "swivel"  or  " clevis"  nuts  to  permit  of  proper 
adjustment.  The  design  of  the  rod- connection  will  depend 
upon  the  section  of  column  or  strut  selected,  but  where  possible, 
the  rod  should  be  bent  and  welded  to  form  an  "eye/1  for  which 
a  "pin-connection"  may  be  provided.  This  style  of  wind- bracing 
is  in  general  use  on  account  of  its  simplicity  and  economy,  but 
in  the  lower  tower  panel,  where  a  diagonal'  rod  might  under 
certain  cases  prove  objectionable,  a  type  called  ''portal-bracing" 
might  be  employed.  A  most  massive,  ornamental,  and  effective 
example  of  this  type  is  seen  in  the  lower  panel  of  the  Eiffel 
tower,  of  Paris.  Its  general  lack  of  utility  for  water  towers 
prevents  its  more  frequent  use,  although  its  adoption  offers  con- 
siderable scope  for  architectural  and  ornamental  effect. 

Anchorage. — The  force  of  the  wind  acting  upon  the  diametral 
plane  of  the  tank  and  the  exposed  tower  surfaces  is  exerted  over 


2O4  TOWERS  AND    TANKS  FOR    WATER-WORKS. 


FIG  58. 


DESIGNING.  205 

a  leverage  which  for  practical  purposes  may  be  considered  as 
being  equal  to  the  height  of  the  tower  and  half  of  the  tank,  and 
produces  the  overturning  moment  of  the  structure,  which  must 
be  resisted  by  the  weight  of  the  metal,  acting  through  a  lever 
arm  equal  to  the  horizontal  distance  from  the  centre  of  the  figure 
at  its  base  to  an  axis  about  the  outer  lines  of  the  base.  When 
the  forces  are  not  in  equilibrium,  anchorage  must  be  provided 
consisting  in  general  of  steel  rods,  two  usually  to  each  tower  leg> 
with  nuts  at  each  end  and  provided  with  a  cast-iron  washer  to 
be  buried  in  the  masonry  pier. 

Graphic  Diagram. — The  capacity  of  the  tank,  the  height  of 
the  tower,  and  other  general  features  having  been  considered 
and  decided  upon,  a  diagram  similar  to  that  shown  in  Fig.  49 
may  be  drawn  to  any  convenient  scale  and  its  principal  dimensions, 
first  indicated.  The  theoretical  thickness  of  the  cylinder  plate, 
web  girder,  and  tank  bottom  are  next  to  be  found  from  formulas 
or  tables  given  heretofore,  after  which  the  details  of  the  cover 
and  balcony  should  be  determined,  illustrations  of  which  have 
been  heretofore  shown,  and  from  all  of  which  the  gravity  loads 
may  be  approximately  calculated  and  the  resulting  stresses  to 
which  the  circular  girder  and  the  supporting  columns  are  sub- 
jected can  be  closely  determined  either  analytically  or  graphically, 
as  may  be  preferred,  and  their  members  properly  proportioned. 
Fig.  59  shows  a  stress  diagram  of  the  loads  for  a  four-post  tower 
of  dimensions  as  indicated  in  the  diagram  (Fig.  58). 

Estimating  Quantities. — Using  these  dimensions  and  pro- 
ceeding according  to  the  formulas  given  in  a  previous  chapter, 
capacities,  areas,  and  quantities  may  be  obtained  as  follows: 

Dimensions  and  Capacities.  Gals.         Pounds, 

Cyl.  20X39  ft.  capacity  =  $$D*A 9I>3^9 

20  ft.  dia.  hem.  bottom,  capacity  =  i.c)6D3 15,680 


Total  capacity  in  gallons 107,049 

Cyl.  2oX  39  ft.  capacity,  49.1  D2A 765,960 

20  ft.  dia.  hem.  bottom  capacity,  i6.$6D3 130,880 

Weight  of  water,  total  pounds 896,81  o 


206  TOWERS  AND    TANKS  FOR    WATER-WORKS. 


>f 


FIG.  59. 


DESIGNING.  207 


SURFACES,    AREAS,    AND   WEIGHTS. 

Dimensions  and  Capacities.  Pounds. 

Cyl.  \  in.  pi.,  xDA  X  10.2 24,990 

5/i6-in.  cir.  girder,  xDAX  12.75 2,405 

5/i6bot.  pi.,  ^Z)2Xi2.76 8,017 

3/16  con.  cover,  %xDA,  sec.  6X7.66 4,144 

3/16  facia  pi.  and  angles,  289X  7.66 2,214 

Eaves  angle,  78.5  X  4.7 369 

5/16  pi.  floor,  3  ft.  wide,  2i68X  12.75 2,764 

8  brackets 1,520 

37-ft.  ladder 242 

3-ft.  Z  trolley 422 

Weight  of  metal 47,087 

10%  allowance  for  overweight 4,708 

Total  weight  of  metal 5*, 795 

Weight  of  water 896,840 


Total  weight  of  tank  and  contents 948,635 

In  addition  to  the  above,  allowance  must  be  made  for  the 
laps  of  plate,  for  the  weight  of  the  rivets,  and  that  of  the  necessary 
flange  angles  and  stiffeners  of  the  circular  girder  and  to  be  exactly 
determined  later,  but  approximated  as  follows: 

Laps 3,000 

Rivets 4,500 

Angles  and  stiffeners 2,500 

Approximated. 10,000 

Stress  in  the  Girder. — The  total  weights  as  found  above 
being  taken  as  958,000  Ibs.  must  be  supported  by  the  circular 
girder,  and  in  this  case  upon  four  points  of  support. 

From  formula  previously  given,  the  bending  moment  of  the 
girder  at  the  point  of  support  where  four  columns  are  used  is 
found  to  be  0.0341  /\Wr,  where  W  is  the  whole  weight  and  r  the 
radius  of  the  tank  in  inches;  substituting,  the  bending  moment  is 

0.034I4X  958,oooX  1 20  =  3,270,61 2  inch-pounds. 


-208  TOWERS  AND    '1ANKS  fOR    WATER-WORKS. 

This  stress  must  be  overcome  by  the  resistance  offered  by 
the  girder  section,  whose  unit  stress  and  modulus  must  be 
found. 

In  the  discussion  of  the  girder,  Carnegie's  formula  for  shear 
strains  was  given,  but  ordinarily  it  is  usual  to  take  10,000  Ibs. 
per  square  inch  of  metal  as  an  allowable  unit  stress,  as  it  is  con- 
sidered good  practice  to  allow  flange  strains  of  15,000  Ibs.  per 
square  inch  and  as  much  as  11,000  Ibs.  of  net  section  for  the 
vertical  shear  of  the  web.  The  modulus  of  resistance,  R,  of  a 
shape  being  its  moment  of  inertia,  /,  divided  by  c,  the  depth  of 
its  neutral  axis,  the  safe  resistance  moment  is  RXS,  or  modulus 
multiplied  by  the  unit  stress. 

The  web  of  the  girder  having  been  previously  found,  the 
other  elements  must  be  obtained  by  trial. 

Deciding  upon  one  top  and  two  bottom  flange  angles  of  di- 
mensions and  placed  as  shown  in  Fig.  48,  their  elementary  areas, 
a,  would  be  as  follows: 

Area. 

2  bottom  angles,  6X 4X  7/16 8.42 

5/i6-in.  X  j6^in.  web 11-25 

Top  angle,  6X4X7/16 4.21 

Total  section  area,  or  la  =  A  — 23.88 

The  distance,  z,  from  an  axis  to  the  centre  of  gravity  of  each 
elementary  area  must  next  be  found.  The  various  handbooks 
give  this  for  numerous  shapes,  some  one  of  which  can  generally 
be  used;  otherwise  special  calculation  is  necessary.  The  quantity 
given  must  be  taken  from  the  length  of  the  lever  arm  of  the  com- 
pound shape  as  measured  from  an  axis  at  one  end  of  the  web, 
or  in  other  words,  from  the  depth  of  the  girder;  in  this  case  from 
36  inches.  The  elementary  areas,  in  the  present  case,  multiplied 
by  their  leverage  is  found  to  be 

8.42X34.03+11.25X18+4.21X4-03  =  506.8, 


DESIGNING.  209 

which  divided  by  the   area  of  the  whole  shape  ^,  =  23.88,  gives 
the  neutral  axis  of  the  girder, 

Sc6.8 
c=  —  ~£  =  2i.2  inches; 

O' 

and  the  moment  of  inertia, 
/,  =  8.36X21.2'  +  6.62  X  21.  22+4.62X  1. 

the  modulus  of  rupture  is 
/ 

*--  or 


and  the  safe  resisting  moment, 

RXS  =  408.4  X  10,000  =  4,084,000  inch-pounds, 

and  to  withstand  a  maximum  bending  moment  at  the  post  ol 
3,270,612  foot-pounds. 

An  angle  with  dimensions  6X4X|  would  have  been  closer  to 
the  requirements,  but  the  difference  in  weight  is  small,  and  since 
the  circular  girder  also  sustains,  in  this  case,  a  small  wind  stress 
beside  and  is  the  most  important  member  of  the  structure,  the 
i/i  6  thicker  angle  will  be  retained,  and  it  is  also  well  to  reenforce 
the  girder  with  stiffening  angles  over  the  point  of  support  as 
shown  in  Figs.  51,  56,  57. 

Wind  Stress  in  the  Girder.—  The  wind  stress  in  the  girder 
is  produced  by  the  action  of  the  wind  upon  the  sides,  and  is 
usually  considered  as  being  exerted  upon  the  diametral  plane  of 
the  cylinder  and  acting  as  a  cantilever  beam,  the  formula  for 

c\  ^  cf  A  ^ 
which  has  heretofore  been  given  as  extreme  fibre  stress  5—  •  , 

where  A=  height  of  cylinder; 

r  =  its  radius  in  inches; 

/  =  the  thickness  of  the  shell. 


210  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

This  stress  is  considerable  in  large  structures  such  as  stand- 
pipes  of  considerable  dimensions,  but  in  the  usual  water-tower 
it  need  hardly  be  considered.  With  the  2oX42-ft.  tank  under 
consideration,  this  stress  is  less  than  500  Ibs.  per  square  inch 
of  metal. 

Torsion  Moment. — The  maximum  torsion  moment  of  the 
girder  for  4  points  of  support  is  found  to  occur  at  an  angular 
distance  of  19°  12'  from  the  point  of  support,  or  in  the  case  under 
consideration,  3.35  feet  along  the  girder,  and  this  stress  can  be 
determined  from  the  formula  given,  viz.,  0.0053^.  Ordinarily 
this  stress  need  not  be  considered  for  tanks  of  the  usual 
capacities. 

Horizontal  Reaction  at  the  Top  of  Posts.— The  total  weight 
being  estimated  as  958,000  Ibs.,  the  vertical  load,  "FT,  at  each  point 
of  support  of  a  four-column  tower  is  239,500  Ibs.,  and  where  the 
angle  of  inclination  of  the  post  is  #  =  7°  59',  whose  tangent  is 
0.14,  the  horizontal  reaction  H,  according  to  the  formula  given 
=  W  tan  6  or  33,530  Ibs. 

As  with  the  gravity  load,  there  is  also  a  horizontal  reaction 
from  the  assumed  wind  stress,  found  by  graphical  analysis  (Fig. 
59)  to  be  7468  Ibs.,  or  a  total  horizontal  thrust  at  the  top  of  each 
post  of  40,998  Ibs.;  where  r=i20  inches,  from  the  formula  and 
table,  the  maximum  bending  moment  at  each  point  of  support 
is  M  =  o.i37,  Hr  =  674,000  inch-pounds,  and  to  resist  which 
the  ring  forming  the  horizontal  flange  of  the  circular  girder  may 
be  used.  Its  elements,  from  the  details  of  Fig.  57,  are  found 
to  be,  moment  of  inertia,  /,  =  3847;  distance  from  neutral  axis, 
£  =  4.03  inches,  and  modulus  of  rupture,  ^  =  954.5.  Assuming 
a  unit  stress  Sy  the  safe  resistance  moment  of  the  shape, 
=  J£X  .$  =  954,500  inch-pounds  as  against  a  maximum  bending 
moment  found  to  be  674,000  inch-pounds;  hence  the  flange  ring 
as  designed  is  well  within  the  limit  of  safety  to  resist  this  reac- 
tion. In  large  structures,  however,  where  the  posts  have  con- 
siderable inclination,  the  'flange  ring  is  often  found  insufficient 


DESIGNING.  211 

alone  to  resist  this  stress  without  considerable  additional  metal, 
and  in  such  cases  it  may  be  necessary  to  employ  a  continuous 
curved  girder  in  the  horizontal  plane. 

Overturning  Moments  at  Points  of  Support.  —  The  over- 
turning moment  of  the  tank  at  its  points  of  support  must  be 
resisted  by  the  connections  of  the  tank  to  the  tower  where  the 
weight  of  the  empty  structure  is  insufficient  to  produce  stability 
of  position,  but  in  general  it  is  always  considered  necessary  to 
rivet  the  flange  of  the  girder  to  the  top  of  the  posts. 

Where  P  =  total  wind  pressure  ; 

G  =  distance  in  feet  from  top  of  post  to  centre  of  gravity; 
M  =  overturning  moment  in  foot-pounds. 

From  the  formula  given,  M  =  PG\  substituting  the  values 
from  the  diagram  (Fig.  58), 


=  958X30=  28,740    and    G  =         -  -=23.4  feet; 


M  =  672,  516  foot-pounds. 

With  the  assumption  that  the  direction  of  the  wind  is  in  the 
direction  of  a  diagonal  in  the  horizontal  plane  of  the  figure  formed 
by  the  posts,  the  tank  would  tend  to  overturning  about  an  axis 
at  the  leeward  post,  and  is  resisted  therefrom  by  the  weight  of 
the  tank  metal  multiplied  by  its  leverage,  or  in  this  case,  by  the 
radius  of  the  tank;  then  M  =  6i,795X  10  =  617,950  foot-pounds. 

Assuming  10,000  Ibs.  per  square  inch  of  rivet  metal  as  a  safe 
value,  each  square  inch  of  metal  would  have  a  holding-down 
value  of  100,000  foot-pounds;  hence  4  rivets,  7/i6-inch  diameter, 
providing  an  area  of  0.61  square  inch,  would  prove  sufficient 
to  establish  equilibrium;  however,  it  is  usual  to  make  these 
connections  of  considerably  larger  diameter,  usually  i-inch  rivets 
being  employed  .and  driven  at  such  points  as  may  be  convenient 
structurally. 


212 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 


Tension  on  the  Joint  between  the  Bottom  and  the  Cylinder. 

— When,  as  in  the  case  under  discussion  (Fig.  48),  the  bottom  is 
a  hemisphere,  the  stress  along  this  joint  is 

— ,     or  —  =  1200  Ibs.  per  linear  inch. 

For    5/i6-inch    bottom    plate,  with  f-inch    rivets,  having   70% 
efficiency  of  joint,  the  strength  of  this  connection  is 


0.3125X60,000X70% 


,    or     3491  Ibs.; 


hence  the  plate   assumed  and  rivets  given  are    ample   to  resist 
the  stress  along  this  joint. 

The  hemispherical  bottom  may  be  composed  of  one  circular 
dished  head  of  steel  plate,  say  96  inches  in  diameter  and  5/16 


FIG.  A. 


inch  thick,  with  ten  5/1 6-inch  curved  special  plates,  all  f  inch 
double  riveted  along  the  vertical  joints,  or  the  segments  may 
be  made  of  such  size  as  may  be  structurally  economical.  The 


DESIGNING.  213 

supply  pipe,  of  required  diameter,  should  be  connected  to  the 
bottom  at  its  lowest  point  by  means  of  a  standard  expansion- 
joint. 

Stress  and  Section  of  Tower  Members.  —  The  determination 
of  the  stress  produced  in  the  tower  by  the  action  of  the  wind  is 
arrived  at  as  follows: 

Taking  wind  in  direction  of  the  diagonal  as  shown  by  arrow 
W  (Fig.  A),  the  maximum  tension  is  produced  in  column  A  and 
the  maximum  compression  in  C;  therefore,  taking  moments 
about  mn,  WH  or  M=VaX  sin  45°+  VCX  sin  45°;  and  as 
Va=Vc,  therefore 

M  M 


This  vertical  force  (Va)  is  resolved  into  its  components,  a 
force  downward  through  the  columns  and  the  horizontal  force, 
which  is  in  turn  resolved  into  two  forces  lying  in  the  planes  of 
the  trusses  AB  and  AD.  The  same  is  true  of  Vc  at  column  C, 
hence  tension  in  A  is  S=  Va  sec.  d,  6  being  angle  of  inclination  of 
post.  Compression  in  C  is  the  same  as  tension  in  A. 

The  horizontal  force  then  is  h  =  Va  tan  0,  and  its  components 
in  the  sides  of  the  tower  marked  R  (Fig.  B)  are 


R=Vat&n6  (.707). 

W 

Having  the  shear  at  the  top  of  each  post,  which  is  —  ,  acting 

4 

in  the  same  direction  as  the  wind,  this  must  be  resolved  into 
forces  lying  in  the  planes  of  the  sides  of  the  tower.     These  are 

W  W 

equal  to  P  =  —  sin  45°  =  —  (.707)  acting  in  direction  shown  by 

arrows  P  (Fig.  C). 

These  forces  must  be  combined  with  the  forces  R,  and  this 
combination  is  shown  in  Fig.  D. 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 


Each  side  of  the  tower  may  now  be  analyzed  graphically,, 
giving  the  stresses  in  the  struts  and  bracing  and  additional  stress 


FIG.  B. 


FIG.  C. 


in   columns;    these   must   be   combined   algebraically  with   the 
stresses  already  found  in  them  to  obtain  the  maximum. 

Solution. 

M  =28,740X23.4  =  672,516  ft.-lbs.; 

.707X672 
a==       14-14 

Sc  =Sa  =  Va  sec 6\  sec  #  =1.01; 

0    =  70.59';  tan  6  =0.14; 

then 

5   =33,625.8X1.01=33,962.06; 


W 

P  =—(.707)  =  5079.79. 
4 

The  wind  stresses  having  been  determined  as  explained  and 
-indicated  on  a  diagram  as  shown  in  Fig.  E,  the  loads  due  to 
the  weights  must  be  considered  and  combined. 


DESIGNING. 


21$ 


The  vertical  gravity  load  at  the  top  having  been  estimated 
at  958,000  Ibs.  for  the  four-post  tower,  the  weight  at  the  top  of 
each  column  is  239,500  Ibs. 

W 

The  vertical  reaction  of  this  load  through  each  post  is  —  sin  6, 

4 

or  239,500X1.01.     This  stress  is  compression  and  must  be  com- 
bined with  the  maximum  compression  at  the  foot  of  the  column 


•  r 

P-R    * 

P 

i 

P-R  =1748.51 

Q. 

P=5079.79 

A                               B 

A                             B 

» 

D                             C 

P=5079.79 

«.              r» 

1 

D                             C 

P-R 

•  1748.51 

P                                                                ? 

FIG.  D. 


FIG.  E. 


and  produced  by  the  wind,  graphically  found  to  be  78,682  Ibs.; 
hence  the  maximum  compression  from  the  combined  gravity 
and  wind  stress  and  exclusive  of  the  weight  of  the  post  itself 
and  dependent  tower  members  is  318,182  Ibs.,  or  159  tons.  It 
is  generally  considered  good  practice  to  limit  the  length  of  any 
section  of  main  posts  to  100  times  its  least  radius  of  gyration, 
and  in  such  case  an  8-inch  rectangular  column,  whose  radius 
of  gyration  is  r=2.3i(r2  =  yV^2)>  might  be  used  in  length  as 
great  as  23  feet.  Having  determined  upon  18  feet  as  the  longest 

section  of  the  tower  column,  —=7.7,  and  from  the  table  according 

to  the  Gordon  formula,  by  interpolation,  the  ultimate  strength 
for  such  length  is  taken  as  32,220  Ibs.;  with  a  factor  of  safety 


2l6  TOWERS  AND    TANKS   FOR    WATER-WORKS. 

of  5  for  tower  members,  the  safe  unit  stress  is  6,444  Ibs.  per  square 
inch,  and  the  metal  required  for  the  column  section  would  be 

-T-^   —  =  49.4  square  inches,  and  which  may  be  secured  by  a 

pair  of  laced  channels  or  other  suitable  combination  of  shapes. 
Determining  to  use  a  Z-bar  column,  according  to  Carnegie's 
handbook,  a  standard  f -inch  column  has  26.3  square  inches,  weighs 
84.1  Ibs.  per  foot  of  length,  and  its  minimum  radius  of  gyration 
is  given  as  2.58,  and  its  safe  bearing  for  lengths  of  18  feet  and 
under  as  157.5  tons.  Since  this  is  the  nearest  section  to  safely 
support  the  given  load,  it  will  be  selected.  With  a  vertical  height 
of  70  feet,  the  inclination  of  the  tower  will  increase  the  length 
of  the  column  beyond  70  feet,  but  the  extra  length  may  be  neglected 
in  determining  the  approximate  weights.  Similarly  the  load  of 
each  pannel  exerts  a  horizontal  stress  which  should  be  combined 
with  that  found  graphically  for  the  compression  stress  due  to 
the  action  of  the  wind,  but  these  loads  being  small,  will  also  be 
omitted.  The  exact  lengths  of  the  horizontal  and  diagonal 
members  of  the  tower  truss  are  hardly  ever  calculated  except 
in  shop  details,  but  are  usually  scaled  from  the  diagram  as  being 
closely  approximate.  In  the  case  under  consideration,  it  will 
be  seen  from  the  diagram  that  the  set  of  diagonal  rods  at  the  top 
of  the  tower  are  subjected  to  the  greatest  stress,  shown  as  9640 
Ibs.  tension.  With  an  allowable  unit  strength  of  12,000  per 

square  inch  of  rod  metal,  the  required  area  is  -       -  =0.8  square 

inch,  or  about  i  inch  round  rod,  which  may  be  adopted  for  all 
of  the  diagonals  in  this  case.  The  first  horizontal  member  from 
the  top  being  in  compression  7060  Ibs.  and  its  length  being  23 
feet,  its  section  must  be  determined.  Commonly  two  channels 
or  four  angles,  riveted  back  to  back,  are  used  for  such  members. 
Selecting  a  pair  of  4-inch  channels,  weighing  5.25  Ibs.  per  lineal 
foot,  from  Carnegie's  handbook,  their  least  radius  of  gyration 
for  neutral  axis  perpendicular  to  their  web  at  centre  is  given 


DESIGNING.  217 

/         23 

as  1.56,  then  —  =  —  ,  =  14.7,  and  from  the  table  (Gordon's  formula) 

their  ultimate  strength  is  approximately  21,320  Ibs.;    their  per- 

21,220 
missible  unit  strength  therefore  is =4265  Ibs.;    then  the 

area  of  the  metal  in  the  section  required  would  be  =1.65 

4265 

square  inches ;  the  area  of  section  for  each  of  the  assumed  channels 
is  given  as  1.55,  hence  for  the  two  the  combined  area  is  3.10,. 
which  is  greater  than  required,  but  since  it  is  economical  con- 
structurally  to  make  all  sections  as  near  alike  as  possible,  when 
differences  are  small,  the  same  size  section  may  be  employed 
throughout  in  each  of  the  pannels.  The  lower  horizontal  member 
having  a  length  of  30  feet  and  its  radius  of  gyration  being  the 
same  (1.56),  its  length,  divided  by  its  least  radius  of  gyration  = 
19.3,  which  from  the  table  gives  an  ultimate  strength  of  ap- 
proximately 16,170  Ibs.,  and  dividing  by  5,  =  3234  Ibs.  permissible 

,    6880 

unit  stress;    the  area  of  the  metal  required  is =2.1,  and 

3234 

since  the  pair  of  channels  selected  have  an  area  of  3.1,  they  would 
be  satisfactory  throughout  for  compression  members.  Scaling 
the  lengths  and  multiplying  by  the  unit  weights  of  rods,  channels, 
and  main  post,  the  additional  weight  at  the  foot  of  the  column 
is  found  to  be  7075  Ibs.  Neglecting  the  slightly  increased  stress 
which  would  be  found  by  multiplying  this  weight  by  the  secant 
of  the  angle,  and  adding  the  weight  directly,  the  total  compres- 
sion in  the  lower  section  of  the  column  is  325,257  Ibs.,  or  162.6 
tons. 

When  a  horizontal  strut  or  tie  is  used  at  the  base  of  the  tower, 
its  weight  must  also  be  included. 

The  horizontal  reaction  H  at  the  foot  of  the  post  =  TF'  tan  6, 
or  325,257X0.14=45,536  Ibs. 

TT 

The  stress  in  each  tie  is  ; —  sec  /?,  or  in  this  square  tower  frame 


21 8  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

22,768X1.41=32,103  Ibs.  For  the  tension  in  this  connection 
and  allowing  10,000  Ibs.  per  square  inch,  the  section  area  =  3. 2 
inches. 

In  smaller  tower  designs,  the  tie  at  the  base  of  the  tower  is 
frequently  omitted,  but  in  which  case  the  horizontal  thrust  H  of 
the  weight  must  be  resisted  by  the  direct  shear  on  the  anchor- 
bolts  and  the  friction  of  the  shoe  on  the  masonry  pier.  There 
is  then  produced  an  overturning  moment  on  the  foundations 
which  must  be  provided  for  in  foundation  design,  in  order  that 
the  resultant  of  the  loads  will  come  in  the  centre  of  the  bearing 
surface  and  avoid  unequal  settlement  of  the  foundations. 

Bearing-plate. — The  thickness  of  the  bearing-plate  when 
made  of  steel,  with  an  allowable  shear  value  of  12,000  Ibs.  per 
square  inch  to  sustain  safely  the  imposed  load  of  325,257  Ibs. 

70  t  2  C7 

applied  by  a  column  section  of  26.3  square-inch  area,  = — -^ — 

I2>367  .     , 

=  —    —  =i  square  inch. 
12,000 

The  other  dimensions  of  the  bearing-plate  must  be  such  as 
to  provide  sufficient  area  to  properly  distribute  the  load  over 
the  masonry  foundation. 

A  stone  sill  or  cap  is  generally  provided,  surmounting  the 
pier  and  directly  supporting  the  bearing-plate.  The  unit  load 
which  it  is  considered  good  practice  to  allow  upon  a  monolithic 
capstone  is  taken  at  from  15  to  30  tons  per -square  foot  of  bear- 
ing, depending  upon  the  character  of  the  stone  used.  Assuming 

70  £  2^7 

20  tons  per  square  foot  as  a  reasonable  average,    —      —  =  8 

40,000 

square  feet,  or  Vii52  =  34X34  inch  plate  required. 

Stability  of  Structure  and  Anchorage. — Investigating  the 
stability  of  the  structure  upon  the  principle  previously  explained, 
with  the  direction  of  the  wind  normal  to  the  side  of  the  square 
formed  by  the  tower  frame,  the  tendency  would  be  to  overturn 
about  the  base  of  the  two  leeward  columns,  and  this  must  be 


DESIGNING.  219 

resisted  by  anchorage  where  the  resisting  moment  is  less  than 
the  overturning  moment.  In  general  it  is  considered  good  policy 
always  to  provide  anchorage,  and  to  design  same  by  considering 
the  weight  only  of  the  empty  structure,  as  the  maximum  wind 
stress  may  occur  at  a  time  when  the  water  has  been  withdrawn 
from  the  tank. 

The  usual  anchorage  consists  of  rods  with  washer  and  nuts, 
the  former  buried  in  the  masonry  and  the  latter  screwed  down 
upon  the  bearing-plate,  through  which  and  the  capstone  the 
rods  project  through  holes  drilled  to  templet.  As  has  been 
explained,  if  the  tie  at  the  foot  of  the  tower  is  omitted,  the  hori- 
zontal thrust  produced  by  the  weight  will'  be  resisted  by  the  shear 
on  the  anchor  rods,  and  this  must  be  considered  in  such  cases 
and  the  dimensions  of  the  rods  fixed  accordingly. 


CHAPTER   X. 
FOUNDATIONS. 

THE  generic  term,  Foundations,  comprehends  both  the 
soil  and  the  materials  upon  which  a  structure  is  designed  to 
rest ;  the  line  of  demarcation  or  termination  of  the  founda- 
tions and  commencement  of  the  substructure  is  variable,  but 
in  general  the  approximate  ground-line  is  the  limiting  point. 
More  exactly,  every  foundation  may  be  regarded  as  having 
two  components — the  bearing-soil,  or  subfoundation,  and  the 
foundations  proper,  consisting  of  the  materials  intended  to 
form  a  solid  base  for  the  superstructure. 

The  preparation  of  the  natural  soil  for  suitable  sub- 
foundations  demands  as  wide  a  consideration  and  treatment 
as  the  wide  difference  of  geological  conditions,  but  in  practice 
an  intimate  knowledge  of  the  varying  soil  characteristics  is 
not  possible  or  hardly  necessary,  and  it  is  considered  suffi- 
cient to  contrast  the  given  soil  with  one  or  more  of  the  more 
common  formations  whose  qualities  are  determined  from  long 
experience.  Such  typical  formations  are  rock,  clay,  gravel 
and  sand,  and  alluvial  soils. 

Rock. — Discussing  these  in  the  order  named,  the  best 
natural  subfoundation  is  rock,  in  classification  varying  from 
the  crystalline  types  to  soft-deposit  specimens,  easily  water- 
worn  or  subject  to  atmospheric  disintegration,  for  experi- 
ence has  shown  that  any  stone  formation,  well  bedded,  will 
safely  sustain  any  load  that  may  be  imposed  upon  it  by  any 
masonry  foundation,  even  for  the  largest  structures. 

220 


FO  UN  DA  TIOKS.  221 

Frequently  the  stone  is  not  found  in  horizontal,  continu- 
ous layers,  but  in  seamy  strata,  offering  a  bearing-surface  of 
more  or  less  irregularity  and  composition.  For  the  suitable 
preparation  of  such  a  subfoundation  the  overlying  earthy 
matter  and  any  decomposed  or  decayed  stone  must  be  re- 
moved to  "  bed-rock"  or  the  solid  layer,  which  is  then  blasted 
or  sledged  to  a  surface  as  nearly  perpendicular  to  the  pressure 
to  be  imposed  as  possible.  Interstices  or  fissures  of  the  rock 
should  be  filled  with  broken  stone  or  concrete,  and  where  the 
bearing  will  not  be  entirely  upon  stone,  but  upon  contiguous 
earth,  at  such  junction  especial  care  should  be  taken  to  thor- 
oughly compact  the  softer  material  or  to  remove  it  altogether, 
substituting  broken  stone,  or  preferably  concrete,  bedded  as 
well  as  possible  to  the  more  unyielding  natural  stone  by  cut- 
ting the  bed-stone  in  steps,  or  making  some  other  effective 
union ;  otherwise  unequal  settlement,  the  result  of  unequal 
resistance,  will  result. 

Clay. — Clay,  when  dry  and  likely  to  remain  so,  is  an  ordi- 
nary and  excellent  foundation,  being  easily  excavated  and 
having  a  safe  bearing- value  for  ordinary  structures;  but  clay 
is  a  treacherous  material  in  that  it  so  readily  absorbs  moist- 
ure, its  seamy  veins  acting  often  as  conduits  for  underground 
streams  of  varying  magnitude.  When  clay  absorbs  water,  its 
tendency  is  to  swell  and  soften,  and  under  such  conditions, 
when  confined,  it  exerts  a  material  pressure  upon  the  sides  or 
bottoms  of  foundations,  tending  to  bulge  and  crack  them. 
When  unconfined  it  spreads  in  every  direction,  oozing  and 
squeezing  from  under  the  weight  imposed  and  becoming  un- 
stable and  uncertain  in  action.  Exposed  to  the  moisture  of 
the  air  it  becomes  more  or  less  saturated,  and  at  low  tem- 
peratures the  mass  freezes,  expands,  and  disintegrates  after  a 
thaw,  proving  a  most  intractable  material.  From  this  fact, 
in  preparing  the  subfoundations  in  such  material,  the  exca- 
vations should  extend  well  below  the  frost-line,  and  the  ex- 


222  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

posure  of  the  foundation-pit  to  atmospheric  influences  should 
be  as  limited  as  possible,  as  a  sudden  rain  may  change  a  good 
foundation  to  a  quagmire.  Excavations  in  clay  should  be 
made  immediately  in  advance  of  the  actual  masonry  con- 
struction. 

When  wet,  the  bearing  value  of  clay  can  be  artificially  in- 
creased and  improved  by  incorporating  with  it,  according  to 
its  plasticity,  layers  of  sand  or  gravel,  or  both,  or  by  spread- 
ing layers  of  concrete. 

The  tendency  of  the  veins  of  the  clay  to  transport  water 
results  in  the  discovery  of  springs  of  water  of  more  or  less 
volume  in  a  number  of  foundation-pits,  and  these  springs  are 
a  source  of  embarrassment  and  trouble,  as  they  prevent  the 
masonry  from  setting,  or  ooze  or  stream  through  the  sides  or 
bottom  of  the  completed  work. 

Their  treatment  is  largely  a  matter  of  personal  experi- 
ence, but  the  less  troublesome  varieties  may  be  suppressed 
by  plugging  the  water-bearing  crevice  with  dry  sand  and 
cement,  dry  cement  or  concrete,  either  directly  or  upon  some 
fibrous  material,  such  as  yarn,  which  will  absorb  the  moist- 
ure until  the  cement  has  an  opportunity  to  set,  or  upon  some 
impervious  material,  such  as  tarred  or  oiled  cloth ;  or  by  set- 
ting a  tube  over  the  aperture,  and  plastering  about  its  foot 
with  pipe-clay,  or  some  plastic  material,  allowing  the  water 
to  rise  in  the  tube,  or  be  drawn  away  through  the  tube  while 
the  masonry  is  being  constructed.  After  the  masonry  has 
set  the  tube  may  be  plugged  with  concrete  below  the  face  of 
the  foundation,  and  then  either  cut  off  or  withdrawn.  These 
are  only  general  suggestions,  experience  being  the  only  safe 
guide  in  such  emergencies. 

Dry  Sand. — Dry  sand  makes  one  of  the  best  subfounda- 
tions  if  its  status  as  such  can  be  fully  determined,  for  it  is  an 
almost  incompressible  body ;  is  not  affected  by  exposure  to 
any  extent,  and  its  bearing  power  is  therefore  very  great. 


FO  UNDA  TIONS.  22$ 

The  size  of  the  grains  of  sand  may  increase  from  very  fine 
particles  to  coarse  gravel ;  the  coarser  the  grain,  the  better 
the  foundation  as  a  rule.  Gravel  and  sand,  when  incorpo- 
rated with  a  binder  of  clay,  are  cemented  together  to  an 
extent  which  makes  such  a  soil  but  little  less  valuable  as  a 
bearing  material  to  the  softer  grades  of  rock,  but  where  the 
grains  of  sand  are  fine,  having  no  cohesion,  the  mass,  when 
saturated  with  water,  becomes  semi-fluid,  and  is  subject  to 
hydraulic  principles.  Owing  to  its  porosity  and  suscepti- 
bility to  moisture,  sand,  like  clay,  is  subject  to  the  disin- 
tegrating effects  of  frost,  and  the  foundation-pits  should 
therefore  be  excavated  below  the  liability  of  such  exposure. 
Also  like  clay,  having  a  capillary  attraction  for  fluids,  in  sand 
foundations,  springs  are  frequently  encountered  which  should 
be  treated  as  above  suggested  in  the  absence  of  more  definite 
knowledge  and  experience.  The  same  methods  would  apply 
for  a  weak  clay  foundation,  such  as  spreading  concrete  over 
the  area  uncovered,  is  advisable  to  assist  and  to  augment  its 
bearing-surface,  but  frequently  in  such  soils,  as  well  as  upon 
the  clay  variety,  the  bearing  values  are  increased  by  remov- 
ing a  portion  of  the  soft  material  and  driving  or  jetting  down 
short  piles  upon  which  stringers  of  wood  are  spiked,  the 
spaces  between  rows  being  filled  with  concrete ;  sometimes 
the  use  of  the  stringers  alone  will  be  found  sufficient  in  addi- 
tion to  the  use  of  the  concrete,  which  is  compacted  flush 
with  the  tops  of  the  sills.  Such  construction  is  called  "  gril- 
lage," and  is  frequently  used.  Since  timbers  covered  by 
water  and  removed  from  atmospheric  oxidation  have  been 
proven  to  last  for  indefinite  periods,  such  a  foundation,  where 
completely  subject  to  saturation,  is  very  effective  and  safe. 
In  very  soft  sand,  clay,  or  alluvial  soils  these  methods  are 
found  effective,  and  in  addition  planking,  making  a  floor  for 
the  foundations  to  be  started  upon,  is  spiked  transversely 


224  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

upon   the    tops   of   the   stringers   and    over  the    concrete    de- 
posited between  them. 

Quicksand. — When  sand  is  so  completely  saturated  as  to 
become  fluid,  it  is  termed  "  quicksand"  ;  it  has  no  peculiar 
qualities  or  inherent  properties,  but  is  generally  given  an 
individual  classification. 

Any  saturated  sand  is  "quick"  when  the  upward  pressures 
of  the  underground  waters  are  sufficient  to  overcome  the 
tendency  of  gravity  to  keep  its  particles  at  rest.  Sand  of 
coarse  grains  resists  this  upward  tendency  to  a  greater  extent 
than  the  finer  varieties;  hence  quicksand  is  usually  a  very 
fine  grained  sand,  and  from  the  fact  that  it  must  be  found 
immersed  in  water,  the  constant  friction  of  its  particles 
moving  upon  each  other  grinds  the  sharp  points  and  angles, 
until  the  grain  becomes  rounded  or  "  water-worn,"  the  usual 
condition  of  the  grains  of  the  so-called  quicksand. 

Increasing  Bearing  Values. — In  very  soft  material,  where 
the  necessity  of  reenforcing  the  bearing-value  of  the  soil  is 
apparent,  and  where  there  exists  an  underlying  soil  of  better 
material,  the  piles,  when  driven  through  the  top  soil,  pene- 
trating into  the  strata  below,  act  as  so  many  columns  whose 
ultimate  bearing  is  the  crushing  strength  of  the  material  of 
which  the  pile  consists,  but  where  there  is  no  such  lower  soil 
the  piles  are  supported  in  the  soft  material  only  by  the  friction 
of  that  material  against  their  sides,  and  the  determination  of 
their  safe  bearing-value  is  more  problematical.  Rankine  gives 
as  a  rule  for  the  safe  bearing  of  piles  under  this  last  condition 
the  area  of  the  head  of  the  pile  in  inches  by  200;  thus  a  12- 
in.  pile,  having  an  area  of  head  of  78  sq.  in.,  would  give  a 
safe  bearing  of  7.8  tons. 

A  simple  rule  frequently  used  for  the  safe  bearing  value 
of  piles  is  one  formulated  by  Major  Sanders,  of  the  U.  S. 
Engineer  Corps,  from  experiments  made  with  common 
wooden  piles  at  Ft.  Delaware,  and  is  as  follows : 


FO  UNDA  TIONS.  22$ 

Weight  of  hammer  in  Ibs.  X  fall  in  inches 

Safe  load  in  lbs.  = 5—; —        —. — : — — r-. 

8  X  penetration  at  last  blow 

Applying  this  rule  to  a  pipe  driven  with  a  224o-lb.  hammer 
and  penetrating,  under  a  2O-ft.  drop,  i  inch,  the  safe  bearing 
in  tons  is  found  to  be  33.6. 

This  value  would  probably  be  considered  too  high. 

A  formula  in  very  general  use  is  one  given  by  Trautwine, 
and  is  used  with  a  factor  of  safety  varying  from  one-half  to  twelve, 
depending  upon  local  conditions.  This  rule  is 

Extreme  |      Cu>  rt>  of  fall  -n  ftXwt  Of  hammer  in  Ibs.  X  0.023 

load  in    >-  =  —  —7—    — r-p : — .     ,         *• 

I  Last  sinking  in  inches +i 

Taking  the  same  constants  as  above,  the  extreme  load  is  128.9 
tons.  Using  a  factor  of  four,  the  result  is  about  as  given  under 
the  Sanders  formula.  Usually  from  18  to  20  tons  is  considered 
a  proper  load  for  a  1 2-inch  pile. 

In  piles  supported  by  the  friction  along  their  sides,  the 
ultimate  value  of  that  friction  is  estimated  at  from  .2  to  I 
ton  per  square  foot  of  bearing  for  each  foot  of  length,  depend- 
ing upon  the  soil  characteristics.  In  silt  or  wet  river-mud, 
when  driven  three  feet  apart,  the  possible  value  of  friction 
upon  unbarked  piles  is  .5  tons  per  foot  length.  In  New 
Orleans,  where  the  soil  is  a  saturated  alluvial  for  900  feet 
depth,  piling  is  used  for  all  building  foundations  where  much 
weight  is  to  be  imposed.  In  some  of  the  larger  buildings, 
even  with  this  addition  to  the  bearing-values,  considerable 
settlement  has  been  observed.  A  foundation  designed  for  a 
stand-pipe,  13  X  100  ft.,  in  that  locality,  consisted  of  100 
piles,  driven  an  average  of  60  ft.  deep,  and  spaced  2  ft.  in 
both  directions.  The  piles  were  of  unbarked  cypress,  aver- 


226 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 


aging  .5  cu.  ft.  per  foot  length.  Although  continuing  to 
penetrate  under  the  blows  of  the  hammer  considerably  more 
than  \  in.,  the  piling  was  stopped  at  60  ft.,  upon  the  theory 
that  the  frictional  resistance  through  that  depth  would  equal 
.5  ton  per  foot  of  pile  length  or  3000  tons  for  the  100  piles. 
Assuming  a  factor  of  safety  of  5>  the  safe  bearing  was  deter- 
mined at  600  tons,  which  represented  the  total  weight  of  the 
tank,  water,  wind-stresses,  and  foundations. 

No  observable  settlement  in  this  foundation  has  taken 
place  in  several  years.  The  piles  were  sawn  and  capped  ;  the 
longitudinal  spaces  were  filled  with  concrete  flush  to  the  top 
of  stringers,  and  the  grillage  floored,  all  timber  being  below 
the  point  of  saturation  of  the  soil.  All  earth  foundations 
must  yield  somewhat,  but  this  is  not  important  in  the  case 
of  isolated  structures  such  as  stand-pipes  and  the  like,  pro- 
vided the  settlement  is  gradual  and  uniform,  and  not  of  radical 
extent. 

The  following  table  represents  the  safe  values  of  ordinary 
soils  according  to  Prof.  Ira  O.  Baker: 

SAFE    BEARING-VALUE   OF    SOILS. 


Kind  of  Material. 

Safe  Bearing-power 
in  tons  per  sq.  ft. 

Max. 

Min. 

Rock,  the  hardest,  in  thick  layers,  in  native  bed  
"      the  softest,  easily  worn  by  water  or  exposure  to 

•• 

200 

18 
4 

2 

I 
8 
4 

2 
0-5 

6 

4 

2 
IO 

6 

4 

i 

Quicksand  and  alluvial  soils  

Stone   Masonry. — The    requirements    for    a    serviceable 
foundation  building  stone  are,  in  the  main,  that  it  shall  be 


FG  UN  DA  TIONS.  22 J 

hard,  tough,  close-grained  and  durable.  Upon  its  closeness 
of  grain  and  nori-porosity  depend  its  non-absorbent  proper- 
ties, without  which  the  stone  is  likely  to  disintegrate  along 
its  layers.  A  stone  with  a  granular  texture  is  likely  to  crumble 
in  weathering  to  a  greater  extent  than  one  with  a  crystalline 
formation.  Before  determining  upon  a  building  stone,  and 
where  a  choice  is  possible,  investigation  as  to  its  possible  use- 
fulness for  the  particular  service  required  should  be  made  by 
an  examination  of  the  effects  of  exposure  and  service  upon 
like  stone  in  any  old  structure,  or  by  an  examination  of  the 
quarry,  where  the  effects  of  weathering  and  decomposition 
should  be  carefully  observed,  noting  whether  the  stone  has 
disintegrated  to  an  appreciable  extent,  or  has  corroded,  or 
whether  the  old  lines  of  fracture  remain  sharp  and  fresh. 
Where  a  new  quarry  is  to  be  opened,  and  there  is  any  doubt 
as  to  the  character  of  the  stone,  it  should  be  subjected  to- 
artificial  tests  such  as  crushing,  abrasion,  etc. 

The  more  common  and  serviceable  building  stones  are 
granite,  limestone  and  sandstone,  in  their  several  varieties. 
The  cost  of  quarrying  such  stone  will  depend  upon  such  fac- 
tors as  the  wages  of  the  quarrymen,  the  mechanical  facilities 
for  such  work,  as  well  as  the  amount  of  "stripping"  neces- 
sary, and  other  items  likely  to  affect  their  cost.  Roughly, 
stone  can  be  quarried  at  from  40  to  80  cts.  per  cubic  yard, 
varying  in  different  localities  and  unlike  conditions. 

Stone  masonry  is  of  various  classes,  but  for  such  foun- 
dation work  as  the  foundations  for  stand-pipes,  it  may  be 
assumed  that  it  will  be  either  ashlar,  range  rubble,  or  rubble, 
laid  in  cement-mortar. 

Ashlar  is  the  highest  grade  of  masonry;  it  is  squared 
dimension-stone,  cut  with  varying  degrees  of  nicety,  and  is 
consequently  considered  as  first  class,  second  class,  etc., 
owing  to  the  finish  required. 

Owing  to  the  care  necessary  for  its  preparation,  it  would 


228  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

hardly  be  employed,  owing  to  its  cost,  upon  any  portion  of  a 
foundation  for  a  stand-pipe  except  possibly  the  first  course 
immediately  below  the  superstructure,  where  such  course  is 
exposed.  Frequently  the  cut  stone  is  used  only  as  a  belt 
upon  the  outer  perimeter  of  the  foundations,  the  interior  or 
core  being  "backed  up"  with  rough  rubble  masonry,  well 
flushed  and  levelled  with  cement.  This  last  type  of  masonry 
consists  of  rubble  proper  and  range  rubble  masonry;  the 
former  being  stone  of  almost  any  dimension,  roughly  sledged 
for  use,  and  bedded  in  cement  without  regard  to  horizontal 
jointing ;  range  rubble  requires  that  the  stone  shall  be  laid  to 
a  rough  line  horizontally ;  the  first  of  these  distinctions  of 
rubble  masonry  is  generally  used  below  the  ground-line  and 
for  the  core  of  the  foundations,  while  the  range  rubble  is  em- 
ployed for  the  exposed  surfaces  up  to  the  first  course  under 
the  structure,  which  is  frequently  of  ashlar  finish.  As  with 
the  quarrying,  the  local  conditions  modify  the  cost  of  all 
masonry  work,  but  roughly  the  following  will  give  an  idea  of 
the  relative  value  of  several  masonry  classifications: 

First-class  ashlar $12.00  to  $15.00  C.  Y. 

Coursed  rubble 4.00  "  6.00  « ' 

Rough  rubble 3.00"  5.00  " 

Concrete — I  part  Port,  cement,  2  sand, 

4  broken  stone 4.00  "  6.00  " 

Ordinary       brick        masonry — cement 

mortar 5.00"  8.00  " 

In  stone  masonry,  Rankine's  general  rule,  modified  to 
suit  particular  conditions  and  individual  ideas,  is  largely  used 
and  is  as  follows : 

RANKINE'S  RULE. 

I.  Build  the  masonry  as  far  as  possible  in  a  series  of 
courses,  perpendicular,  or  as  nearly  so  as  possible,  to  the 


FOUNDATIONS. 


229 


direction  of  the  pressure  which  they  have  to  bear;  and  by 
breaking  joints  avoid  all  long  continuous  joints  parallel  to 
that  pressure. 

II.  Use  the  largest  stones  for  the  foundation  course. 

III.  Lay  all  stones  which  consist  of  layers  in  such  manner 
that  the  principal  pressure  which  they  may  have  to  bear  shall 
act  in  a  direction  perpendicular,  or  as  nearly  as  possible,  to 
the  direction  of  the  layers.      This  is  called  laying  the  stone  on 
its  natural  bed,  and  is  of  primary  importance  for  strength  and 
durability. 

IV.  Moisten  the  surface  of  dry  and  porous  stones  before 
bedding  them,  in  order  that  the  mortar  may  not  be  dried  too 
fast  and  reduced  to  powder  by  the  stone  absorbing  its  mois- 
ture. 

V.  Fill  all  parts  of  every  joint,  and  all  spaces  between  the 
stones,  with  mortar,  taking  care  at  the  same  time  that  such 
spaces  shall  be  as  small  as  possible." 

From   various    authorities   the    following   table   has  been 
compiled  : 

SAFE    BEARING-VALUE    OF    MASONRY    AND    MODULUS     OF    RUPTURE    OF 
MATERIALS. 


Mod.  of  Rupture 
per  Sq.  In. 

Crushing-   Strength 
per  Sq.  Ft.,  in  Tons. 

1800 

7c 

I5OO 

62    < 

o-jaS 

I*7    ^ 

2l6o 

60  o 

Concrete,    i    month,    i   part  Port,  cement, 
2  parts  sand,  and  4  parts  broken  stone.. 
Brick  laid  in  Port,  cement,  I  to  2  mortar... 
"        "      "  Rose'le     "          i  to  2  mortar.. 

ISO 
800 
800 

7.0 
IO.O 

8.0 

Brick  Masonry. — There  is  no  generally  recognized  manu- 
facturers' standard  brick,  the  general  character  and  dimen- 
sions varying  considerably  in  different  localities,  but  an  average 
size  is  8y  X  4"  X  2j"  ;  such  brick,  when  dry,  will  weigh  about 
5  pounds  each,  and  in  rough  reckoning  500  such  brick  are 


230  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

estimated  as  making  a  cubic  yard  of  masonry,  which  weighs 
approximately  1.2  tons.  With  such  brick  an  ordinary  mason, 
with  one  helper,  will  lay  2000  in  foundations.  In  such  work, 
below  the  surface,  the  brick  can  be  rapidly  placed  in  courses 
and  then  grouted  in  by  "  slushing"  cement-mortar  over  the 
surface,  which  fills  the  interstices  and  makes  a  bed  for  the 
succeeding  course;  in  such  foundations  bats  may  be  used  in 
moderate  numbers.  At  the  ground-line  more  care  is  taken, 
and  the  brick  are  laid  to  a  horizontal  line,  those  forming  the 
face  being  carefully  laid,  and  the  mortar-joints,  which  should 
not  be  over  ^  in.  thick,  are  <4  struck"  and  neatly  pointed.  A 
good  foundation-brick  should  be  of  close  clay  texture,  well 
made,  hard,  and  carefully  burned.  When  two  such  brick  are 
struck  smartly  together  they  should  give  a  clear,  metallic  ring. 
Foundation-brick  should  not  absorb  more  than  about  7  per 
cent,  of  their  weight  of  water  after  immersion  for  24  hours. 
The  color  of  a  brick  is  no  index  of  its  qualities,  although 
where  the  clay  soil  contains  oxide  of  iron  the  color  of  the 
brick  after  burning  will  be  red,  and  a  good  foundation-brick 
will  be  a  "  cherry-red."  Obviously,  the  bearing- value  of 
brick  varies  with  the  texture  of  the  material,  its  care  in 
making  and  burning,  and  the  skill  with  which  it  is  erected 
into  masonry  when  bonded  with  a  suitable  mortar.  As  shown 
by  table,  page  158,  the  safe  bearing-value  of  brick  masonry, 
in  cement-mortar,  is  taken  at  from  8  to  10  tons  per  square 
foot,  and  experience  has  shown  this  to  be  a  safe  and  conserva- 
tive value.  Numerous  tests  have  been  made  upon  piers 
erected  under  different  conditions  by  the  United  States  gov- 
ernment and  individuals,  but  it  is  doubtful  whether  such 
experiments  are  of  much  practical  value. 

While  in  no  wise  conclusive,  the  failure  of  a  brick  pier 
and  the  collapse  and  total  destruction  of  a  tower  and  tank 
designed  by  the  author,  gives  an  opportunity  to  present  cer- 
tain facts  in  that  connection  which  may  assist  in  throwing 


FOUNDATIONS.  23! 

some  light  upon  the  ultimate  resistance  of  brick  masonry 
under  normal  and  actual  conditions. 

Below  the  ground-surface,  with  a  bearing-soil  of  good,  stiff 
clay,  four  piers  of  6  ft.  base  and  2  ft.  square  tops,  construc- 
ted of  sound,  hard-burned  Georgia  clay,  laid  in  a  mortar  con- 
sisting of  i  part  Belgian  cement  and  2  parts  sharp  road-sand, 
and  into  each  of  which  two  anchor-rods  ij  ins.  diameter  with 
12  X  f-in.  boiler-plate  washers  had  been  inserted,  had  been 
constructed  for  the  support  of  a  13-ft.  diameter  by  25-ft. 
high  steel  water-tank,  supported  by  a  four-column  tower, 
40  ft.  in  height.  Upon  the  detail  drawings  a  24  X  24-in. 
cap  was  shown,  but  owing  to  a  misunderstanding  as  to  who 
was  to  furnish  this  bearing-plate,  the  cap  was  not  provided. 
A  delay  in  securing  the  necessary  anchor-rods  from  the 
manufacturer  resulted  in  the  purchase  by  the  assistant  en- 
gineer of  a  set  of  ij-in.,  5-ft.  rods,  supplied  with  the  12  ins. 
square  boiler-plate  washers.  Later,  when  the  original  rods 
were  received,  accompanying  them  was  a  set  of  12  X  i8-in. 
washers,  which,  through  the  carelessness  and  ignorance  of 
the  assistant  engineer  and  the  erecting  foreman,  were  set  on 
top  of  the  foundations  to  serve  as  bearing-plates  for  the 
tower.  The  piers  were  completed  exactly  45  days  before 
the  final  test,  at  which  time  the  tank  was  filled  within  2  feet 
of  its  top,  when  the  foundations  gave  way  and  the  whole 
structure  failed. 

The  weight  of  the  material  was  28,000  Ibs.,  the  weight  of 
the  water  at  62^  Ibs.  per  cu.  ft.  was  192,000  Ibs.,  the  approxi- 
mate weight  of  each  pier  was  9,000  Ibs.  At  the  time  of  the 
failure  there  was  no  wind  blowing,  so  that  the  total  weight 
applied  as  compression  was  256,000  Ibs.,  or  128.0  tons.  With 
the  24  X  24-in.  cap  specified,  the  bearing  upon  the  masonry 
would  have  been  8  tons  per  square  foot. 

Under  the  conditions  at  the  initial  moment  of  failure,  the 
entire  weight  of  the  tank  and  load,  amounting  to  no  tons, 


232  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

was  concentrated  upon  the  12  X  i8-in.  washer  used  as  a  cap, 
and  this  downward  tendency  was  resisted  by  the  holding-down 
power  of  three  12  X  12-in.  washers  in  the  three  other  piers, 
or  a  total  of  648  square  inches.  Investigations  made  after 
the  failure  show  that  the  excessive  weight  caused  the  column 
to  puncture  the  pier  through  its  entire  length,  coring  out  and 
completely  crushing  the  brickwork  contained  between  the  two 
anchor-rods,  representing  an  area  of  about  14  or  15  ins.  square. 
Immediately  below  this  core,  the  brick  footings  were  intact, 
and  a  solid  section  14  X  15  ins.  was  buried  or  driven  into  the 
bearing-soil  of  clay.  The  masonry  around  the  column,  which 
had  penetrated  into  the  solid  masonry  about  3!  feet,  was  not 
crushed,  but  was  ruptured  radially  along  the  cement-mortar 
joints.  Before  the  failure  the  piers  were  tested  both  with  an 
engineer's  and  mason's  spirit-level,  and  were  checked  as  being 
truly  horizontal  and  of  the  same  height.  The  resistance  offered 
by  the  subfoundation-soil  to  the  penetration  of  the  14  X  I5~in. 
section  of  footing  course  might  be  considered  as  amount- 
ing to  10  tons,  and  to  that  extent  reducing  the  weight  applied 
as  downward  pressure  at  the  initial  moment  of  rupture ;  under 
this  supposition,  the  ultimate  bearing  of  the  masonry  was  IOO 
tons  -T-  4.5  =  22.2  tons.  Although  45  days  had  elapsed 
since  the  completion  of  the  piers,  the  cement-mortar  in  the 
centre  of  the  pier  had  not  fully  hardened  and  was  rather 
crubbly,  although  that  exposed  to  the  atmosphere  nearer  the 
surface  was  well  set  and  very  tenacious.  After  the  failure 
the  piers  were  torn  away  and  new  foundations,  built  upon  the 
original  dimensions,  were  substituted,  and  upon  a  24  X  24-in. 
cast-iron  cap  the  structure  was  built  according  to  original 
design  and  has  been  perfectly  stable  during  the  past  two  years. 
Concrete  Foundations. — In  general  engineering  work,  con- 
crete is  a  most  useful  material.  It  is  formed  of  broken  stone 
from  f-  in.  to  2  ins.  in  longest  diameter,  of  gravel,  broken 
brick,  shells,  etc.,  the  voids  of  the  mass  being  filled  with 


FO  UN  DA  TIONS.  233 

cement-mortar  of  various  proportions,  depending  upon  the 
ratio  of  voids  of  the  material.  In  practice,  a  good  concrete 
can  be  made  with  one  part  of  cement,  two  parts  sand,  and 
four  parts  broken  material.  In  foundation-work,  a  good  grade 
of  Portland  cement,  sharp  sand,  and  clean  stone  should  be  in- 
sisted upon.  The  volume  of  water  used  to  incorporate  the 
mass  is  the  subject  of  never-ceasing  discussion  amongst  the 
engineering  fraternity,  but  in  the  author's  practice  a  good 
concrete  has  been  made  by  so  dampening  the  mixture  that 
after  being  deposited  and  rammed,  a  slight  appearance  of 
water  upon  the  surface  is  all  that  is  necessary.  Concrete  for 
small  foundations  is  usually  mixed  by  hand,  upon  a  12  X 
12-ft.  frame  or  light  platform,  the  ingredients  being  placed 
conveniently.  A  proportion  of  sand,  by  measure,  is  first 
spread  over  the  board  into  which  is  dumped  the  specified 
proportion  of  cement,  and  the  two  components  thoroughly  in- 
corporated by  the  workmen  with  their  shovels ;  spreading  this 
mixture  so  that  it  shall  be  somewhat  higher  along  the  outer 
edges  of  the  mixing-board,  water  is  sprayed  from  a  small  hose 
upon  the  mass,  which  is  quickly  turned  with  shovels  until  every 
particle  has  been  completely  incorporated.  Into  this  liquid 
paste  the  proper  proportions  of  stone,  after  a  drenching,  are 
added,  and  quickly  turned  by  the  laborers  until  each  particle 
of  stone  has  been  coated  with  the  mortar.  The  concrete  is 
then  carefully  deposited  by  the  shovels  of  the  workmen,  in 
layers  from  3  to  6  ins.  thick,  into  the  foundations.  Such 
mixing  and  spreading  by  hand  will  cost  approximately  60  cts. 
per  cubic  yard ;  the  cost  of  the  concrete  will  depend  upon 
varying  conditions,  and  will  range  from  $4.00  to  $6.00  per 
cubic  yard  in  place. 

Maximum  Pressures. — The  action  of  the  wind  upon  the 
cylindrical  surface  of  a  tank  and  the  application  of  that  force 
as  pressure  upon  the  base  has  been  previously  explained. 
The  normal  pressure  due  to  the  load  is  the  weight  divided  by 


234  TOWERS  AXD    7^ANKS  FOR    WATER-WORKS. 

the  area,  and  the  maximum  pressure  to  be  transferred  to  the 
subfoundations  will  consist  both  of  the  normal  and  variable 
pressures.  From  the  principles  of  resistance  of  materials, 
previously  explained,  the  ;<live  load"  or  variable  pressure 
due  to  the  wind  can  be  found  from  the  formula 

Ml 
Wind  pressure  =  — j  ; 

and  the  maximum  pressure  will  therefore  be 

W       Ml 

Max.  pressure  — r-  -J j- ; 

A          2.1 

where  M  =  moment  of  the  wind  ; 

/  =  the  leverage  at  the  base ; 

7  =  moment  of  inertia  of  the  shape. 

Where  it  becomes  necessary  to  extend  the  base  of  a 
foundation  in  order  not  to  overload  the  bearing  soil,  the 
foundations  will  extend  in  regular  courses,  and  the  safe  pro- 
jection of  the  successive  courses  will  depend  upon  the  pres- 
sure applied  as  force  and  the  resisting  quality  of  the  material 
of  which  the  courses  are  composed. 

The  theory  of  this  action  and  resistance  is  given  by  Prof. 
Ira  O.  Baker,  in  "A  Treatise  of  Masonry  Construction,"  and 
is  as  follows : 

"  The  area  of  the  foundation  having  been  determined  and 
its  centre  having  been  located  with  reference  to  the  axis  of 
the  load,  the  next  step  is  to  determine  how  much  narrower 
each  footing-course  may  be  than  the  one  next  below  it. 
The  projecting  part  of  the  footing  rests  as  a  beam  fixed  at 
one  end  and  uniformly  loaded.  The  load  is  the  pressure  on 
the  earth  or  on  the  course  below.  The  set-off  of  such  a 
course  depends  upon  the  amount  of  the  pressure,  the  trans- 
verse strength  of  the  material,  and  the  thickness  of  the 
course. 


FO  UNDA  TIONS.  235 

"To  deduce  a  formula  for  the  relation  between  these 
quantities, 

let  P  =  the  pressure  in  tons  per  square  foot  at  the  bottom  of 

the  footing-course  under  consideration  ; 
R  =  the  modulus  of  rupture  of  the  material  in  pounds  per 

square  inch  ; 
/  =  the  greatest  possible  projection  of  the  footing-  course 

in  inches; 
t  =  the  thickness  of  the  footing-course  in  inches. 

"  The  part  of  the  footing-course  that  projects  beyond  the 
one  above  it  is  a  cantilever  beam  uniformly  loaded.  From 
the  principles  of  the  resistance  of  materials  we  know  that  the 
upward  pressure  of  the  earth  against  the  part  that  projects 
multiplied  by  one-half  of  the  length  of  the  projection  is  equal 
to  the  continued  product  of  one-sixth  of  the  modulus  of  rup- 
ture of  the  material,  the  breadth  of  the  footing-course,  and 
the  square  of  the  thickness.  Expressing  this  relation  in  the 
above  nomenclature  and  reducing,  we  get  the  formula 


or  with  sufficient  accuracy,  /  = 


This  represents  a  theoretical  maximum  set-off  for  the  masonry 
courses,  but  in  practice,  as  has  been  explained,  it  is  usual  to 
reduce  this  theoretical  maximum  allowance  by  a  suitable  fac- 
tor of  safety,  and,  in  this  particular,  a  factor  of  safety  of  5  to 
10  is  customary  and  considered  a  safe  practice. 

In  addition  to  the  forces  acting  upon  the  foundation-soil, 
the  material  of  which  the  actual  substructure  will  consist 
adds  its  weight  to  the  other  forces  as  pressure  upon  the  sub- 
foundations,  and  therefore  a  general  knowledge  of  the  weight 
of  different  varieties  of  masonry  is  necessary.  On  the  following 
page  will  be  found  a  tab^  giving  the  approximate  weights  of 


236  TOWERS  AND    TANKS  FOR    WATER-WORKS, 

the  several  building  materials  most  generally  used  in  stand- 
pipe  foundation-work  and  compiled  from  various  recognized 
authorities : 

WEIGHT    OF    MASONRY    IN    TONS    PER    CUBIC    YARD. 

Weight  of  granite  or  limestone,  dressed  throughout  (ashlar).   2.2  tons. 

"         "        "        "          "  rough  rubble 1.8     " 

"         "  sandstone,  ashlar 1.9     " 

"         "       "         "        rubble 1.6     " 

Brick  masonry,  medium  work 1.6     " 

Ordinary  concrete 1.4     " 

Designing  Foundations,  Including  Anchorage  and  Cap- 
ping.— To  design  a  suitable  foundation  for  a  particular  struc- 
ture the  normal  weight  must  first  be  determined  or  assumed. 

Considering  a  proper  design  for  a  stand-pipe  24  ft.  dia.  X 
1 20  ft.  in  height,  and  whose  actual  weight  was  considered  as 
80  tons,  and  whose  dimensions  would  add  1696  tons  as  the 
weight  of  the  water,  or  a  total  of  1776,  and  which  weight 
should  be  first  considered  as  acting  over  a  base  equal  to  the 
area  of  the  structure,  or  452.4  sq.  ft.,  or  with  a  unit-stress 

W       1776 

equal  to  «j-  or——  =3.9  tons  per  sq.  ft. 
A        452-4 

Neglecting  for  the  moment  the  weight  of  the  foundations, 
and  which  can  only  be  obtained  after  a  suitable  design  has 
been  determined  upon,  to  secure  the  maximum  pressures  per 
unit  of  bearing-surface,  in  addition  to  the  normal  weight  di- 
vided by  the  area,  there  must  be  added  the  forces  due  to 
flexure  or  to  the  effect  of  the  wind  upon  the  cylindrical  sides 
of  the  stand-pipe  and  as  applied  through  its  leverage  to  the 
base  and  over  the  area  to  be  covered  by  the  foundations. 

Substituting  the  proper  values  in  the  formula  — j- ,  or  for 

a  cylindrical  figure  24  ft.  dia.  X  120  ft.  in  height,  and  taking 
30  Ibs.  per  sq.  ft.  of  diametral  surface,  as  has  been  ex- 
plained, as  the  action  of  the  wind  upon  the  sides  of  the  cylin- 
der, the  force  exerted  by  this  variable  quantity  is 


FO  UNDA  TIONS.  2$? 

2592X12 


32572 
while 

W 


=    .9  tons  per  sq.  ft., 


or  a  total  of 4.8  tons  per  sq.   ft.    of  bearing. 

If,  after  suitable  tests,  the  soil  was  considered  capable  of 
sustaining  this  load,  the  foundations  could  be  carried  verti- 
cally, and  directly  under  the  structure  without  any  "spread,"' 
and  in  such  a  case  only  a  sufficiency  of  masonry  need  be  pro- 
vided to  secure  a  proper  anchorage,  and  intended  simply  to 
resist  the  overturning  moment,  without  increasing  the  bear- 
ing-area. In  such  a  case,  the  stability  of  the  structure  having 
been  determined  by  the  principle  of  moments,  as  has  been 
explained,  and  a  sufficient  number  of  rods  provided  to  pre- 
vent the  overturning  of  the  structure,  the  holding-down 
power  of  these  rods  must  be  secured  by  designing  for  each 
rod  a  "washer"  or  bearing-surface,  upon  which  a  sufficient 
load  could  be  imposed  in  the  shape  of  masonry  as  to  resist 
the  effects  of  the  horizontal  action  of  the  wind  tending  to 
overturn  the  structure  at  its  toe. 

Now  this  overturning  moment  has  been  found  to  be 
approximately  2592  ft. -tons,  while  the  resisting  moment,, 
being  80  tons  of  material,  multiplied  by  its  leverage,  12  ft., 
is  960  ft. -tons,  leaving  an  excess  overturning  moment  of 
1632  ft. -tons  which  must  be  resisted  by  designing  some  form 
of  anchorage. 

The  load  which  the  anchorage  is  required  to  resist  is 
found  by  dividing  the  excess,  1632  ft. -tons,  by  the  leverage 
of  the  anchorage,  in  this  case  say  12  ft.  ;  hence  the  com- 
bined strength  of  the  anchorage  to  prevent  overturning  is 
136  tons,  and  the  strength  required  of  each  rod  is  found  by 
dividing  this  product  by  the  number  of  rods. 


238  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

Since  the  area  of  a  circle  represented  by  the  base,  24  ft. 
diameter,  is  452.4  sq.  ft.  for  ordinary  brick  masonry  whose 
weight  is  1.6  tons  per  cubic  yard,  each  vertical  foot  of  foun- 

1  ^  ^  *J 

dation    weighs    26.88    tons,  therefore       .,      •  =  6    ft.    as    the 

20.00 

height  of  the  substructure. 

As  has  been  explained,  the  anchorage  consists  usually  of 
iron  or  steel  rods  set  in  the  masonry  and  bolted  to  some 
external  shapes  riveted  to  the  superstructure.  Such  rods 
receive  their  holding-down  or  resisting  stresses  from  flat 
washers  supported  by  the  bolt-head  of  the  rod  and  acting 
against  the  masonry  above,  and  must  be  designed  of  size  and 
strength  sufficient  to  prevent  their  being  bent  downward  or 
broken  off,  and  with  a  surface  sufficiently  broad  to  prevent 
the  masonry  from  giving  way,  thereby  permitting  the  washer 
and  bolt  to  crush  the  masonry  and  pull  through,  and  their 
bearing-area  must  therefore  be  such  as  to  distribute  the  ap- 
plied load  over  a  sufficient  portion  of  the  masonry  to  prevent 
overloading  and  crushing. 

If  ten  rods  and  washers  were  provided  as  anchorage  and 
with  a  leverage  of  12.5  ft.,  each  rod  would  bear  T1¥  of  the 
total  applied  stress,  in  this  case  y1^-  of  1632,  or  163.2  ft. -tons, 
and  this  divided  by  their  leverage,  12.5  ft.,  each  rod  and 
washer  must  be  designed  to  resist  13  tons  pressure,  or  a  total 
stress  of  26,000  Ibs. 

Such  washers  are  usually  of  cast  iron  with  a  unit  maxi- 
mum shear  value  of  20,000  Ibs.  per  sq.  in. 

The  safe  bearing-value  of  masonry  as  taken  from  the 
table  being  approximately  10  tons  per  sq.  ft.  or  144  sq. 
in.,  for  brick,  the  area  of  the  washer  to  resist  the  applied 

stress  would  be — ,  or  187.2  sq.  in. ;   and  if  a  circular 

washer  were  used,  its  diameter  would  be  about  15  to  16  in. 
and  the  unit-stress  140  Ibs.  per  sq.  in.  over  the  surface.     The 


FO  UN  DA  TIONS.  239 

transverse  strength  of  such  a  plate  or  washer  depends  upon 
its  thickness,  and  an  exact  formula  is  difficult  to  arrive  at, 
but  that  used  by  Kidder  is  probably  upon  the  safe  side,  and 
is  as  follows : 


I W  X  P' 

Thickness  of  plate  in  inches  =  \  / 

y 


where  W  is  the  unit  load  per  square  inch — in  the  present  case 
140  Ibs. ;  P,  the  projection  of  the  edge  of  the  plate  beyond 
the  rod,  in  this  case  say  6.5  in.  Substituting  these  values  in 
the  formula,  the  thickness  of  the  cast-iron  plate  or  washer  is 
a  little  less  than  2  in.  at  its  thickest  part  next  the  rod. 

As  a  rule,  the  bearing-value  of  the  soil  will  seldom  be 
considered  safe  for  a  load  as  great  as  that  considered  above, 
and  the  bearing-value  of  the  soil  must  be  increased  by 
spreading  the  foundations  over  a  greater  area. 

In  order  to  consider  such  a  condition,  assume  that  the 
bearing-value  of  the  soil  is  not  over  2  tons  per  sq.  ft,  of  sur- 
face, and  that  the  same  conditions  exist  as  were  considered  in 
the  preceding  example.  Let  the  safe  bearing  2  tons  be  rep- 

W  W 

resented  by  B,  and  B  =  — r;  then  A  =  -=-.      Let  A   be  the 

A  Jj 

total  area  and  £Fthe  total  load. 

The  total  constant  weight  of  the  tank  and  water  was 
found  to  be  1776  tons;  the  wind-pressure,  approximately  I 
ton  per  sq.  ft.,  exerted  over  an  area  of  452  sq.  ft.,  adds  452 
tons ;  while  the  weight  of  the  masonry  was  estimated  at  about 
27  tons  per  vertical  foot,  and  for  6  feet  amounts  to  162  tons, 
or  a  total,  W,  of  2390  tons.  Substituting  this  value  for  W 

W 
in  the  formula  A  =  -^-,  the  required   area   of   base  is  about 

39  feet ;  but  spreading  the  base  increases  the  weight  of  the 
foundations,  therefore  some  greater  diameter  must  be  selected 


240  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

and  determined  by  experiment.  In  order  to  allow  for  a  mar- 
ginal projection  for  the  anchor-rods,  the  perimeter  of  the 
upper  plane  of  a  conic  frustum,  which  is  a  suitable  form  for 
the  foundation  of  a  stand-pipe,  might  be  that  for  a  27-foot- 
diameter  circle,  which  would  allow  an  annular  space  of  18  ins. 
around  the  24-ft. -diameter  tank.  If  such  a  conic  section  is 
considered  in  cross-section,  the  lower  base  projects  beyond 
the  upper  with  a  length  equal  to  half  the  difference  on  either 
side,  and  this  projection,  representing  the  spread  of  the 
masonry,  is  secured  by  offsets  in  the  masonry  courses,  the 
number  and  height  of  such  offsets  determining  the  height  of 
the  figure  or  foundations. 

As  shown,  the  maximum  theoretical  projection  may  be 

determined  from  the  formula/  —  \tv~p  '•>  and  if  the  masonry 

is  in  courses  of  brick  whose  thickness,  /,  is  2.5  in.,  with  a 
modulus  of  rupture  R,  according  to  the  table,  of  800  Ibs., 
and  a  pressure  at  the  base,  P,  of  2  tons,  substituting  these 
values  in  the  formula,  the  maximum  theoretical  offset  is  8.3 
an.,  to  be  reduced  by  the  use  of  a  suitable  factor  of  safety. 

The  maximum  safe  projection  of  brick  in  single  courses, 
as  determined  by  practice  and  ordinance  in  many  cities, 
is  J  the  length  of  a  single  brick,  or  a  fraction  over  2  ins.,  or  a 
factor  of  safety,  using  the  formula  above,  of  4,  which,  having 
been  used  in  designing  throughout,  will  be  continued  in  foun- 
dation work  where  the  masonry  is  an  almost  solid  monolith. 

For  experiment,  selecting  a  44-ft. -diameter  circle  as  the 
required  base,  the  projection,  being  the  difference  between 
that  and  the  2 /-ft.  diameter,  or  17  ft.,  the  projection  on 
either  side  is  102  ins.,  and  the  projection  allowed  for  each 
course  being  2  ins.,  there  are  51  projections,  whose  thickness 
being  2.5  inches,  the  height  of  the  foundations  is  10.6  feet. 
From  these  quantities  the  exact  total  weight  can  be  deter- 
mined, and  is  as  follows : 


FO  UNDA  TIONS.  24 1 

Constant  weight  of  tank  and  water , .   1776  tons 

Wind-pressure  exerted  over  foundation-base 517     " 

Whight  of  masonry   634     " 

Total  applied  weight  and  stress 2927  tons 


Then  if  B}  or  allowable  bearing- value,  =Wt  total  weight 
•or  2927,  -T-  A,  total  area  or  1520,  the  actual  bearing  under  the 
•given  conditions  is  1.92  tons,  or  a  bearing  slightly  less  than  the 
assumed  safe  bearing-value  of  the  soil. 

In  designing  the  foundations  for  a  tower  and  tank,  the  same 
formulae  and  methods  are  employed.  To  determine  the  wind 
stress,  however,  the  moment  of  inertia  7  is,  of  course,  that  of  a 
rectangle  or  polygon,  with  sides  bounding  the  figure  formed 
by  the  base  of  the  tower  instead  of  that  for  a  circle. 

The  supporting  column  of  a  tower  must  be  provided  with  a 
footing  or  pedestal  at  its  base.  This  should  consist  of  a  steel 
base  plate,  reinforced  by  angle  connections  and  securely  riveted 
to  the  tower  post.  Holes  of  proper  area  must  be  drilled  for 
.anchor  rods. 

The  bearing-plate  is  subjected  to  direct  shear  from  the  total 
load  concentrated  and  delivered  by  the  metal  of  the  column 
cross-section,  and  its  unit  stress  should  not  be  less  than  10,000 
pounds  per  square  inch.  In  water-towers  of  small  capacity 
the  area  of  the  bearing-plate  may  be  made  sufficient  to  safely 
distribute  the  load  directly  to  the  masonry,  or  a  cast-iron  cap 
may  be  provided,  in  either  case,  with  area  great  enough  to  dis- 
tribute the  load  upon  the  bearing  surface  so  that  it  shall  not 
-exceed  100  pounds  per  square  inch  pressed. 

Generally,  however,  it  is  considered  more  desirable  and  orna- 
mental to  surmount  the  piers  with  a  capstone. 

When  this  is  specified  the  stone  should  be  a  monolith,  sound 
and  of  close  texture,  preferably  granite;  its  bearing  surfaces 
at  least  should  be  "patent-hammer"  dressed.  An  empirical 
rule  for  its  dimensions  is  that  its  lowest  bearing  surface  must 


242  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

be  such  as  to  provide  sufficient  area  to  transmit  the  whole  im- 
posed load  to  the  masonry  without  stress  greater  than  100  pounds 
per  square  inch,  and  its  depth  should  not  be  less  than  f  times 
its  length  thus  determined. 

The  bearing  surfaces  of  all  stones  should  be  truly  horizontal 
when  set  and  the  depth  of  each  stone  should  exactly  correspond. 

Rod  holes  for  anchorage  must  be  carefully  drilled  from  tem- 
plets. 

According  to  Baker,  the  crushing  strength  and  weights  of 
different  stones  are  as  follows. 

Max.  Tons  Wt.  per 

per  Sq.  Foot.  C.  F. 

Granite 1510  178 

Limestone 1440  1 74 

Marble 1440  180 

Sandstone 1080  175 

In  practice  it  is  safe  to  assume  the  bearing  value  of  single 
stones  at  from  15  to  30  tons,  depending  upon  their  characteristics- 

The  dimensions  of  the  masonry  pedestals  must  in  each  case 
be  determined  by  the  character  of  the  bearing  soil  of  the  sub- 
foundations  and  the  extent  of  the  load  to  be  applied;  in  other 
words,  the  base  of  the  pedestal  must  be  spread  so  as  to  provide 
a  safe  bearing  and  this  spread  will  govern  the  height.  Where 
the  tower  design  fails  to  provide  for  ties  connecting  adjacent 
posts,  the  horizontal  thrust  of  inclined  posts  must  be  resisted 
by  the  anchorage,  and  when  thus  resisted,  the  thrust  produces 
an  overturning  moment  in  the  pier  which  must  be  considered 
and  provided  for,  usually  by  additional  spread  of  the  base,  which 
produces  a  corresponding  increased  load  and  resistance. 


CHAPTER   XL 

PAINTING,    - 

Discussion. — A  lay-writer  has  clearly  defined  the  science 
of  engineering  as  "  Common  sense,  directed  by  theory  and 
practice,  to  works  of  construction,"  and  he  might  have  added 
"  whose  comparative  permanency  was  a  prime  consideration." 

This  last,  as  a  desideratum,  it  seems  is  frequently  omitted 
by  the  engineer  as  well,  and  content  with  selecting  materials 
and  designing  members,  scant  consideration  is  given  to  the 
necessity  for  effectually  preserving  the  works  of  his  creation 
when  once  they  have  been  completed  and  tested. 

Engineers'  specifications  for  the  protective  coating  for 
iron  or  steel  too  often  exhibit  a  variability  which  permits  al- 
most anything  in  the  nature  of  paint  to  be  applied  as  a  pre- 
servative, provided  it  is  not  too  expensive,  dries  quickly, 
covers  the  ordinary  stains,  and  for  a  time  looks  well. 

A  more  satisfactory  explanation  is  to  attribute  this  neglect 
to  a  lack  of  knowledge  rather  than  to  a  lack  of  interest,  which 
is  more  to  be  condoned  in  view  of  the  absolute  diversity  of 
opinion  of  those  recognized  as  authorities  as  to  what  consti- 
tutes the  best  method  of  protecting  metallic  structures  from 
corrosion  and  decay,  and  the  further  fact  that  possibly  in  the 
practice  of  the  individual  he  has  developed  the  anomalous 
idea  that  the  cheapest  paints  have  at  times  evinced,  in  actual 
use,  superior  qualities  to  scientifically  correct  and  high-priced 
compounds. 

A  communication  was  received  a  short  time  since  from  a 

243 


244  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

well-known  authority  upon  the  manufacture  and  properties  of 
structural  steel  in  reply  to  a  request  for  his  opinion  as  to  the 
best  protective  coating  for  steel,  in  which  he  says  that  he 
11  knew  no  more  about  it  than  the  average  engineer.  This 
is  equivalent  to  saying  that  I  know  nothing,  for  there  seems 
to  be  a  radical  difference  of  opinion  on  this  question,  and  one 
engineer  will  claim  that  one  kind  of  material  is  the  very  best 
thing  that  can  possibly  be  used,  and  the  next  man  will  claim 
that  it  is  the  very  worst.  It  reminds  me  of  the  investigation 
made  by  the  L.  A.  W.  Bulletin  on  the  "  Best  Lubricant  for  a 
Bicycle."  They  published  their  conclusions,  which  ran  about 
as  follows: 

1.  Vaseline  is  the  best  lubricant. 

2.  Vaseline  is  no  earthly  good." 

Considering  the  immense  and  increasing  amounts  of  iron 
and  steel  used  annually  as  structural  materials  for  marine 
work,  buildings,  trusses,  bridges  and  the  like,  and  the  limited 
and  conflicting  knowledge  of  the  best  methods  of  protection, 
it  is  surprising  that  accidents  are  not  more  frequent  and  seri- 
ous, and  that  coroners'  juries  are  not  more  often  called  upon 
to  render  similar  verdicts  to  that  given  in  investigating  a  cele- 
brated bridge-failure  and  accident,  where  the  jury  found  that 
41  All  went  in,  none  came  out,  and  there  is  nothing  to  sit  on." 

Iron-rust. — Although  the  best  methods  of  preventing 
corrosion  may  be  involved  in  uncertainty  and  dispute,  the 
cause  of  the  destruction  of  ferric  members  seems  to  be  fairly 
well  established  and  it  is  a  generally  accepted  scientific  theory 
that,  primarily,  rust  or  metallic  corrosion  is  the  effect  of  a 
chemical  combination  of  carbonic  acid  gas,  oxygen,  and  water 
with  metallic  iron,  producing  ferric  oxide  or  iron-rust  which, 
once  affected,  continues  with  great  rapidity  through  both 
chemical  and  galvanic  action. 

It  has  been  shown  by  frequent  experiment  that  carbonic 
acid  gas  and  oxygen,  together  or  separately,  will  not  pro- 


PAINTING.  245 

duce  the  phenomenon  of  rusting  until  water  is  added  to  com- 
plete the  compound.  Fresh  water  alone,  when  free  from 
acids  or  organic  impurities,  has  been  found  to  have  but  little 
effect  upon  submerged  plates  of  bright  iron  or  steel,  but  where 
the  plate  is  entirely  or  intermittently  immersed  in  salt  water, 
the  salt  water,  taking  the  iron  oxides  into  solution,  removes 
the  oxides  and  exposes  fresh  metallic  surfaces  to  attack,  also 
setting  up  a  voltaic  action  upon  ferric  bodies. 

Structural  work  is  generally  exposed  only  to  atmospheric 
action,  the  atmosphere  being  sometimes  charged  with  salt- 
sea  vapors,  and  always  with  some  moisture,  in  addition  to 
the  three  universal  components — nitrogen,  oxygen,  and  car- 
bonic acid  gas — in  the  presence  of  which  the  destruction  of 
ferric  members  is  sure ;  the  intensity  and  extent  of  this  action 
being  directly  dependent  upon  the  quantities  of  each  element 
entering  into  the  chemical  action. 

Chemical  and  Galvanic  Action. — The  chemical  reaction 
in  such  cases  is  the  setting  free  of  the  hydrogen  of  the  water, 
its  oxygen,  uniting  with  the  carbonic  acid  and  metal,  forming 
ferrous  carbonate,  which  again  combining  with  the  oxygen  of 
the  water  or  atmosphere,  is  decomposed  into  ferric  oxide  and 
carbonic  acid  gas,  the  latter  passing  off,  leaving  the  sesqui-oxide 
of  iron  to  absorb  and  condense  water,  becoming  the  hydrated 
sesqui-oxide  of  iron  whose  symbol  is  2(Fe*  O^H^O,  ordinarily 
known  as  iron-rust. 

It  is  a  familiar  fact  that  bright  iron  or  steel  may,  under 
favorable  conditions,  be  kept  unprotected  free  from  rust  for  a 
considerable  time,  but  that  when  once  the  process  of  rusting 
commences,  the  rust  specs,  as  centres  of  corrosion,  rapidly 
spread  until  the  entire  metallic  surface  becomes  covered  with 
a  sheet  of  rust.  The  chemical  explanation  of  this  progressive 
action  when  rusting  has  once  commenced  is,  that  during  the 
decomposition  by-oxidation  of  the  ferrous  carbonate  to  ferric 
hydrate,  the  enlffe  amount  of  carbonic  acid  is  not  given  off, 


246  TOWERS  AND   TANKS  FOR    WATER- WORKS. 

and  acts  upon  the  new  surfaces  of  the  metallic  iron,  and 
owing  to  the  porous  and  hygroscopic  character  of  the  rust 
crust,  only  small  quantities  of  oxygen  and  moisture  are  neces- 
sary to  indefinitely  continue  the  process,  the  hydrated  oxide 
giving  no  protection  to  the  underlying  metal.  The  capacity 
of  rust  for  absorbing  and  condensing  moisture  and  oxygen  is 
enormous,  and  it  has  been  proved  that  iron-rust  will  absorb 
as  much  as  27  gallons  of  oxygen-gas  in  making  one  pound  of 
rust. 

It  seems  beside  the  strictly  chemical  action,  there  is  a 
galvanic  effect  which  augments  the  work  of  corrosion  and 
destruction  when  once  begun ;  for  it  has  been  shown  that  the 
oxides  of  any  metal  are  electro-negative  to  the  metal  itself, 
and  that  in  ferric  oxide  a  voltaic  action  is  set  up  in  its  fibres 
and  surfaces  in  contact  by  thermo-electric  currents  due  to 
changes  of  temperature  of  the  body ;  further,  that  the  contact 
of  such  products  as  iron  and  steel  is  sufficient  to  set  up  such 
action,  the  result  being  a  pitting  and  corrosion  of  the  material, 
now  technically  known  as  electrolysis ;  and  it  has  been  asserted 
that  the  difference  in  the  molecular  arrangement  of  the  same 
materials — due  either  to  manufacturing  methods  which  result 
in  lack  of  homogeneity,  or  from  the  unequal  application  of 
force  as  stress  that  changes  the  arrangement  of  the  fibres — is 
sufficient  to  produce  voltaic  destructive  action. 

Mill-scale. — In  rolling  iron  or  steel,  the  scale  sometimes 
left  upon  the  surface  of  the  metal,  and  known  as  "  mill-scale," 
has  been  analyzed  as  sesqui-oxide  of  iron,  Fe*O\  the  same  chem- 
ical composition  as  ordinary  iron-rust,  and  it  seems  further  to 
possess  to  the  same  marked  degree  the  capacity  for  absorption 
and  condensing  moisture  and  oxygen,  producing  corrosion 
and  decay,  and  setting  up  galvanic  action,  the  effect  appearing 
in  rust-cones  pitting  and  eating  the  metal. 

It  is  asserted  that  where  mill-scale  is  left  upon  plates  of 


UNIVERSITY 

CF 


PAINTING.  247 

steel  its  effect  upon  the  neighboring  bared  metal  is  as  strong 
and  continuous  as  copper  would  be  in  its  galvanic  action. 

Overwhelming  testimony  and  positive  evidence  have 
proven  the  following  facts : 

1st.  That  rust  and  mill-scale  exert  a  most  destructive 
action  upon  iron  and  steel. 

2d.  That  where  moisture  and  carbonic  acid  gas  accumu- 
late in  considerable  quantities,  the  rapid  destruction  of  ferric 
bodies  follows. 

3d.  That  rusting,  once  started,  progresses  rapidly  even 
under  what  seems  a  perfect  protective  covering. 

4th.  That  if  a  covering  can  be  found  which  will  prevent 
the  penetration  of  moisture,  the  perfect  protection  of  the 
metal  is  assured  so  long  as  the  covering  remains  intact. 

In  1882  exhaustive  experiments  were  conducted  by  author- 
ity of  the  British  Admiralty,  resulting  in  the  following  con- 
clusions : 

(i)  That  no  pitting  occured  in  mild  steel  when  freed  from 
mill-scale ;  (2)  that  the  loss  of  weight  from  corrosion  of  clean 
mild  steel  and  clean  iron  did  not  differ  greatly ;  and  (3)  that 
the  action  of  mill-scale  is  considerable  and  continuous,  and 
equal  to  a  similar  quantity  of  copper  in  its  corrosive  action 
due  to  galvanism. 

In  long  tunnels  in  which  accumulations  of  carbonic  acid  gas 
and  moisture  are  found,  and  as  exampled  by  the  Arlberg,  St. 
Gothard  and  Musconetong  tunnels,  the  life  of  iron  or  steel 
work  is  very  brief,  and  a  renewal  every  few  years  has  been  a 
necessity;  in  the  last  of  these,  it  is  reported  that  the  /6-lb. 
steel  rail  was  removed  after  five  years'  service  and  was  found 
to  have  lost  more  weight  by  corrosion  than  by  use. 

The  continuous  action  of  rust  is  clearly  shown  by  a  report 
to  the  French  Naval  Office  as  to  the  effect  of  rust  upon  several 
torpedo-boats  which  had  never  been  put  .into  commission,  but 
were  laid  up  undercover  and  painted  at  intervals.  An  inspec- 


248  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

tion  showed  that  the  plates  under  the  paint  were  so  corroded 
that  the  blow  of  a  testing-hammer  was  sufficient  to  puncture 
them,  and  that  large  areas  under  the  paint-film  were  so  affected. 
This  same  effect  of  the  continuous  action  of  rust  has  been  ob- 
served in  the  repair  of  numerous  bridges  and  other  structures, 
when  the  metal  was  found  entirely  destroyed  under  the  paint- 
coating.  A  large  truss-roof  that  was  kept  constantly  painted 
having  failed,  it  was  found  that  the  metal  was  simply  rotten 
with  rust  under  the  paint,  while  no  appearance  of  the  insta- 
bility of  the  structure  from  this  cause  was  apparent  to  the  eye. 
The  same  result  is  recorded  by  builders  in  the  case  of  floor- 
beams  which  were  practically  eaten  away  below  the  paint-sur- 
face. 

A  recent  investigation  by  Mr.  D.  H.  Maury,  of  the  elec- 
trolitic  injury  to  the  metal  of  the  Peoria,  111.,  stand-pipe  is  of 
great  interest,  and  is  given  as  follows : 

"  On  March  30,  1894,  the  water  company's  steel  stand- 
pipe  on  the  West  Bluff  burst,  killing  one  person  and  injuring 
15  others,  one  of  whom  died  later  from  his  injuries.  Upon 
examining  the  wreck  of  the  stand-pipe,  the  writer  at  once 
noticed  a  peculiar  pitting  of  the  inside  of  the  vertical  sheets, 
and  the  appearance  of  these  pits  was  so  different  from  that 
caused  by  any  ordinary  oxidation  that  he  was  soon  almost 
positive  that  they  were  due  to  electrolytic  action.  A  similar 
stand-pipe  on  the  East  Bluff  was  drained,  and  was  found  to  be 
similarly  pitted.  The  whole  inner  surface  of  the  vertical  shell 
appeared  to  be  thickly  covered  with  blisters,  resembling  in 
outward  appearance  the  tubercles  sometimes  found  inside  of 
old  cast-iron  mains. 

"This  blistered  covering,  which  was  almost  as  thin  as- 
paper,  was  composed  entirely  of  oxide  of  iron,  and  on  brush- 
ing it  away  with  the  finger-tips,  the  black  paint  with  which 
the  stand-pipe  had  been  originally  coated  would  be  found 
beneath  it. 


PAINTING.  249 

"The  black  paint  was  oftentimes  almost  unbroken,  or  at 
least,  very  slightly  cracked.  When  the  paint  was  brushed  off, 
the  pit  would  be  disclosed,  considerably  smaller  in  area  than 
the  surface  covered  by  the  blister.  The  surface  of  the  metal 
in  the  pit  was  perfectly  bright  and  clean,  and  its  fibre  was 
clearly  discernible. 

"Many  of  these  pits  were  more  than  -§•  in.  in  depth.  They 
were  slightly  more  numerous  in  the  West  Bluff  stand-pipe, 
and  were  in  both  generally  larger  and  deeper  on  the  lower 
courses  of  the  vertical  shell.  .  .  .  The  East  Bluff  stand-pipe 
was  distant  about  60  ft.  from  the  street-railway  line  on  Bour- 
land  Street.  The  West  Bluff  stand-pipe  was  about  700  ft.  dis- 
tant from  the  railway  line  on  Knoxville  Avenue.  Both  stand- 
pipes  were  more  than  a  mile  from  the  power-station,  and  were 
negative  to  the  rails.  The  electrical  examination  relative  to 
the  stand-pipes  was  conducted  mainly  at  the  East  Bluff  stand- 
pipe,  which  was  still  in  service.  A  flow  of  a  part  of  the  cur- 
rent from  the  railway  line  was  clearly  traced  through  the  earth 
to  the  anchor-bolts  which  held  the  stand-pipe  to  its  founda- 
tions, up  these  bolts  and  into  the  steel  of  the  shell,  and 
through  the  shell  and  from  its  inner  surface  to  the  projecting 
section  of  the  i6-in.  flanged  cast-iron  pipe  which  served  as 
both  inlet  and  outlet,  and  which  connected  the  stand-pipe  to 
the  water-mains.  The  current  was  then  traced  along  this 
pipe  and  along  the  mains  to  the  power-station.  The  deflec- 
tion of  the  volt-meter  needle  was  clearly  traced  to  the  rail- 
way current,  being  especially  influenced  by  the  one  or  two 
cars  on  the  line  beyond  the  stand-pipe  on  Knoxville  Avenue, 
and  when  the  cars  stopped  running  at  night,  the  movement 
of  the  needle  ceased.  Where  the  current  left  the  inner  sur- 
face of  the  shell  to  pass  through  the  water  of  the  inlet-pipe  it 
made  the  pits  already  described.  These  stand-pipes  and 
the  inlet-pipes  were  negative  to  the  rails,  and  are  striking  ex- 
amples  of  electrolytic  pitting  under  such  conditions." 


2$0  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

From  the  history  of  the  Peoria  stand-pipe,  it  having  been 
noted  that  the  specifications  called  both  for  iron  and  steel  as 
structural  materials  and  desiring  to  ascertain  whether  galvanic 
or  battery  action  might  not  have  been  the  result  of  the  iron  and 
steel  in  contact  in  the  presence  of  moisture,  the  author  wrote 
Mr.  Maury,  receiving  a  reply  in  which*he  stated  that  he  did 
not  think  anything  but  steel  plate  had  been  used  in  the  con- 
struction of  the  stand-pipe,  except  the  rivets,  and  possibly  the 
ladder  and  some  connections;  that  careful  investigations 
looking  for  battery  action  were  made,  but  this  action  had  not 
been  substantiated. 

Cleaning  the  Metal. — It  having  been  shown  and  demon- 
strated that  it  is  of  prime  necessity  to  prevent  the  commence- 
ment of  the  rusting  process  in  its  incipiency,  and  that  the  first 
consideration  is  to  provide  for  the  thorough  cleaning  of  the 
metal  before  an  attempt  is  made  to  give  it  a  protective  cover- 
ing, it  is  in  order  to  discuss  the  methods  employed  for  this 
process  of  cleaning  or  preparation  for  painting. 

For  this  purpose  there  are  three  processes  in  vogue  and  in 
general  use.  One  is  by  "  pickling";  another  by  the  use  of 
the  sand-blast,  and  a  third  and  more  general  method  is  by 
scraping  and  cleaning  with  wire  brushes. 

The  pickling  process  consists  in  the  submersion  of  the 
plate  or  shape  in  a  bath  of  hydrochloric  or  sulphuric  acid  for 
a  period  of  one-half  to  twenty-four  hours,  and  afterwards 
neutralizing  the  acid  by  the  use  of  lime,  the  lime  then  being 
cleaned  off.  The  proportions  of  acid  to  water  range  from  10 
to  19  parts  of  water  to  I  of  acid,  the  latter  being  the  formula 
adopted  by  the  British  Admiralty.  Such  a  method  of  clean- 
ing plates,  while  reasonably  economical  and  convenient,  and 
fully  effective  when  carefully  performed,  is  open  to  the  objec- 
tion that  any  carelessness  upon  the  part  of  the  workmen  is  sure 
to  produce  results  which  are  worse  than  the  proposed  cure. 
The  second  method  of  cleaning  metallic  surfaces  is  a  mechani- 


PAINTING.  251 

cal  one,  sharp-grained  sand  being  employed  under  about  15 
pounds  compressed-air  pressure  at  the  nozzle,  to  cut  away  the 
rust  and  mill-scale,  by  being  directed  to  the  desired  point 
from  the  end  of  a  rubber  tube  or  hose.  While  a  certain 
method  of  cleaning  when  intelligent  care  is  exercised,  and  the 
penalty  for  negligence  not  being  so  severe  as  where  acid  is 
used,  the  objection  recorded  to  the  use  of  sand* is  that  a 
special  building  must  be  provided,  from  the  fact  that,  unless 
the  sand  is  confined,  it  is  likely  to  prove  damaging  to  ma- 
chinery and  become  generally  a  nuisance. 

The  last  and  most  popular  method  of  cleaning  plates  and 
shapes  is  by  the  use  of  scrapers  and  brushes,  either  by  hand 
or  mechanically,  electric  revolving  brushes  being  considerably 
used  of  late.  The  loosened  material  is  wiped  away  with  oiled 
waste  or  rags.  Nearly  all  of  the  larger  bridge-works  clean  their 
shapes  in  this  way.  The  objection  to  this  is  that  although 
the  surfaces  may  seem  bright  and  free  from  rust  and  scale, 
under  a  glass  it  will  be  seen  that  only  the  microscopic  met- 
allic points  have  been  burnished,  the  depressions  showing 
minute  rust-specks  which  have  not  been  touched  by  the  scraper 
or  brush,  and  may  therefore  become  points  or  foci  for  corro- 
sion. For  these  reasons,  it  would  seem  that  specifications  for 
the  cleaning  of  metals  should  be  drawn  to  include  the  use  of 
the  sand-blast,  the  cost  of  which  is  about  the  cost  of  a  coat  of 
good  paint,  and  is  said  to  be  about  $1.50  per  ton  of  metal, 
exclusive  of  handling.  During  its  evolution,  the  time  at 
which  the  metallic  member  should  be  cleaned  and  primed  is 
of  great  importance.  In  an  investigation  of  this  question, 
a  testing-bureau,  having  a  wide  experience  and  facilities  for 
observation,  writes  as  follows:  "  In  rolling  a  plate,  a  slab  is 
drawn  from  the  heating-furnace  or  soaking-pit,  and  it  passes 
through  the  rolls.  As  it  is  being  reduced,  salt  is  thrown  upon 
the  slab;  it  causes  a  loud  explosion,  and  loosens  the  scale 
formed  and  a  steam-jet  is  turned  on  the  slab,  which  blows 


252  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

this  scale  off,  so  the  finished  plate  comes  with  no  scale  upon  it 
to  the  cooling-beds.  In  the  rolling  of  angles  and  similar 
shapes  it  is  not  possible  to  do  this.  Therefore,  there  is  more 
scale  upon  the  angles  than  on  plates.  After  rolling,  shapes 
are  as  a  rule  stacked  immediately  upon  loading-beds  prepara- 
tory to  shipment,  it  being  against  the  mill's  policy  to  hold 
material  any  longer  than  it  is  necessary  to  get  cars  and  to 
load.  Shapes  after  they  come  from  the  strengthening-press, 
which  is  directly  after  cooling,  are  not  under  cover.  In  case 
of  plates,  the  conditions  are  different.  After  the  plates  are 
rolled  they  have  to  be  laid  off  and  sheared  to  size,  and  then 
stacked  up  awaiting  shipment.  In  the  majority  of  cases  this 
is  always  under  cover.  Open  cars  are  nearly  always  used  in 
shipping  steel,  on  account  of  the  convenience  in  loading  from 
cranes  and  also  on  account  of  the  variation  in  lengths."  The 
above  explains  the  processes  and  evolution  at  the  mills,  and  in 
order  to  arrive  at  the  condition  at  which  the  material  reaches 
the  shops,  inquiry  was  made  of  a  large  boiler  and  metal-work- 
ing establishment,  located  from  600  to  700  miles  from  the 
point  of  metal-supply.  They  write:  "We  find  very  little 
rust,  mill-scale,  or  grease  on  any  of  the  sheets  coming  from  the 
mills;  though  we  must  confess  we  find  much  more  now  than 
we  used  to  heretofore.  .  .  .  There  is  a  big  difference  in  the 
steel  plate  from  the  different  mills;  there  is  a  gloss  or  finish 
upon  some,  while  from  another  mill  they  appear  red,  as  though 
they  were  rusted.  Now  any  of  these  plates  will  stand  the 
weather  without  being  injured  or  rusted,  especially  the  ones 
best  finished,  and  it  is  not  necessary,  in  our  opinion,  to  paint 
or  oil  the  plates  at  the  mill.  The  effect  of  rolling  plates  after 
they  were  painted  would  be  to  scale  off  much  of  the  paint." 
From  such  testimony  it  appears  that,  under  ordinary  circum- 
stances, it  is  not  necessary  to  protect  plates  at  the  mill  by 
painting  or  priming,  and  that  at  the  shop  the  mechanical 
work  of  rolling  to  radius,  as  for  boiler  and  stand-pipe  plate,. 


PAINTING.  253 

and  the  punching  and  handling  of  untreated  plates  and  shapes, 
as  well  possibly  as  the  jar  of  railway  transportation,  and  the 
several  handlings,  loosen  more  mill-scale  than  enough  to  com- 
pensate for  any  rusting  in  transit,  and  that  therefore  the 
proper  time  to  clean  and  prime  is  at  the  shop,  after  the  me- 
chanical work  has  been  completed,  and  immediately  before 
shipment  to  the  point  of  erection,  any  grease  which  may  re- 
sult from  the  machining  being  also  subject  to  removal  at  the 
same  time.  The  facilities  for  cleaning  and  painting  being 
usually  superior  at  the  shop  to  those  likely  to  obtain  at  the 
point  of  erection,  is  another  consideration  in  favor  of  shop- 
cleaning  and  priming.  Structural  metal,  when  carefully 
cleaned  of  all  rust,  mill-scale,  grease,  and  dirt,  should  be  im- 
mediately protected  by  some  covering  as  nearly  impervious  to 
moisture  as  possible  in  order  to  prevent  further  corrosion 
from  chemical  and  galvanic  action. 

Zinc  Coating. — It  has  been  found  that  the  application  of 
molten  zinc,  called  ''spelter,"  as  a  bath,  forms  a  coating 
which  is  electrically  positive  to  iron  or  steel,  and  which  in 
the  presence  of  galvanic  action  results  in  the  corrosion  of 
the  zinc  and  the  protection  of  the  ferric  body.  Such  a  coat- 
ing is  very  effective,  but  with  the  larger  plates,  where  the 
dipping  is  done  by  hand,  the  process  is  very  expensive,  -f-  in. 
plate  being  the  thickest  material  so  far  galvanized  for  practi- 
cal purposes,  the  cost  being  from  $14.00  to  $16.00  per  ton. 
Besides  the  expense,  unfortunately  the  process  reduces  the 
strength  of  plates  and  shapes  to  an  extent  that  galvanized 
metal  is  generally  considered  as  being  "  rotten  "  and  unfit  for 
use  where  certain  and  considerable  strength  is  required. 

Again,  it  has  been  asserted  that  water  in  galvanized  re- 
ceptacles or  reservoirs  becomes  unfit  for  use,  which,  if  true, 
would  debar  this  method  of  protection  either  for  the  towers 
and  members  where  strength  was  required,  or  for  the  tank, 
where  the  storage  of  water  was  the  purpose  of  the  structure. 


254  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

A  small  municipal  water-supply  plant  in  use  in  California  has 
two  small  galvanized  tanks  in  service,  which  seem  to  have 
given  satisfaction. 

"  Oxidized  Plates. " — Another  method  of  treating  steel 
or  iron  plate  for  protection  against  corrosion,  popularly  called 
"  oxidizing,"  has  been  accomplished  in  several  ways  with  sat- 
isfactory results,  the  effect  being  produced  by  heating  the 
metal,  and  afterwards  subjecting  it  in  a  furnace  to  the  action 
of  mingled  steam  and  carbonic  acid  gas,  resulting  in  the  pro- 
duction upon  the  metallic  surface  of  a  coating  of  the  black 
oxide  of  iron,  FeaO3FeO. 

It  is  claimed  that  the  same  result  has  been  obtained  by 
coating  the  metal  with  a  mixture  of  red  oxide  of  iron,  con- 
taining an  almost  equal  amount  of  silica  and  in  a  solvent  of 
resin-oil,  and  afterwards  heating  the  metal  to  a  bright  red.  It 
is  also  claimed  that  the  metal,  heated  to  about  300  degrees 
Fahr.,  and  immersed  in  an  asphaltum  mixture  of  the  same 
temperature,  will  produce  the  same  black  oxide  coating,  but 
in  this  case  it  would  seem  that  the  plate  must  first  have  com- 
menced to  rust  naturally,  to  produce  the  change  from  red  to 
black  oxide.  In  some  of  these  processes,  the  change  in  the 
strength  of  the  material  is  not  more  than  that  which  would  be 
produced  by  annealing,  but  in  the  first  of  these  methods  it  is 
certain  that  the  iron  or  steel  is  permanently  expanded,  which 
would  be  a  certain  advantage.  The  protective  power  of  the 
black  oxide  film  or  coating  is  shown  from  the  record  of  an  iron 
column,  said  to  have  been  erected  at  Delhi,  India,  about  900 
B.C.,  and  which  is  60  ft.  in  height  and  weighs  about  17  tons. 
After  the  lapse  of  ages,  the  surface  is  free  from  rust  and  other- 
wise unaffected  by  weathering. 

Japanned  Plates. — A  permanent,  hard  and  enamel-like 
coating,  capable  of  successfully  resisting  the  effects  of  corro- 
sion, is  known  as  "japan,"  and  is  produced  by  treating  the 
article  to  be  protected  to  a  composition  consisting  of  asphalt 


PAINTING.  255 

and  linseed-oil,  as  a  base,  with  copal  resin,  thinned  with  tur- 
pentine, subjected  afterwards  to  a  slow  heat  in  an  oven  or 
furnace,  a  process  of  baking.  Trays,  ornaments,  door-locks 
and  knobs,  and  small  articles  have  been  successfully  treated 
to  this  process,  and  of  late,  experiments  upon  a  larger  scale 
have  been  made. 

Practical  Considerations. — While  the  adoption  of  such 
processes  is  known  to  afford  more  effective  preventatives  to 
metallic  corrosion  than  any  other  method  of  covering  so  far 
developed,  the  effect  upon  the  metal  itself,  the  cost  and  in- 
convenience of  operation,  and  the  necessity  of  especial  appli- 
ances would  seem  to  debar  such  means  from  practical  and 
general  use  for  the  protection  of  structural  material,  fre- 
quently in  heavy  masses;  depending  for  its  usefulness  upon 
its  certain  and  known  strength,  and  whose  manufacture,  com- 
mencing at  the  mill,  continuing  at  the  shop,  and  possibly 
proceeding  at  remote  points  of  erection,  seems  to  permit  the 
employment  of  no  means  which  is  not  simple,  convenient, 
speedy,  and  economical,  which  conditions  are  more  nearly  ful- 
filled by  the  protection  afforded  metals  through  paint-films, 
and  it  would  therefore  appear  that,  comparatively,  they  are 
the  best  protective  coverings  for  iron  or  steel.  As  such  agent, 
the  records  of  the  past  leave  much  to  be  desired,  and  it  should 
therefore  be  the  serious  effort  of  all  engineers  or  other  scien- 
tists, both  chemists  and  physicists,  to  continue  in  an  effort  to 
develop  this  protective  agency  to  the  highest  attainable 
degree. 

Paint-films. — Paint  is  used  for  purposes  of  ornamenta- 
tion as  well  as  for  protection,  but  only  in  the  last  of  these 
functions  will  it  be  considered  here,  where  the  practical, 
rather  than  the  aesthetic,  is  the  prime  consideration. 

Paint  is  a  film  of  one  or  more  coats  or  thicknesses,  which 
may  be  applied  or  spread  with  a  brush  over  any  surface,  and 


256  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

primarily  consists  of  a  liquid  as  the  vehicle  or  medium,  with 
which  a  base,  or  pigment,  is  in  combination  or  solution. 

A  perfect  paint  should  be  tenacious;  non-corrosive;  elas- 
tic; impervious;  of  easy  application;  of  reasonable  covering 
and  drying  qualities,  and  of  comparative  economy. 

The  usual  causes  of  the  destruction  of  the  paint-films 
when  applied  to  such  structures  as  metallic  iron  or  steel  tanks 
are  expansion  and  contraction  of  the  metal ;  sand  or  other 
sharp  particles;  or  rain  and  sleet,  contained 'in  gusts  of  wind 
impinging  upon  the  paint-film  ;  the  chemical  and  galvanic  ef- 
fect of  light  and  heat,  in  the  presence  of  moisture  and  gases, 
and  acting  upon  the  paint-substances;  the  lack  of  adhesion  of 
the  film  to  the  metal,  usually  caused  by  the  presence  of  moist- 
ure upon  the  metallic  surface  previous  to  the  application  of 
the  film,  resulting  in  "  peeling,"  and  finally  the  destructive 
action  of  the  water  enclosed  in  the  tank  upon  the  oil,  causing 
swelling,  shrivelling,  disintegration,  and  a  slumping  away  of 
the  film. 

Linseed-oil. — However  much  individuals  may  disagree  as 
to  the  character  of  the  pigment,  linseed-oil  as  a  medium  or 
liquid  vehicle,  which  has  been  used  since  the  remote  ages, 
continues  the  standard  of  efficiency. 

Linseed-oil  is  a  product  obtained  from  grinding  flaxseed 
to  a  coarse  meal,  which  is  heated  and  sacked,  and  being 
placed  under  powerful  presses,  the  oil  is  extracted  in  a  crude 
shape,  and  is  refined  by  sedimentation  and  filtration  extend- 
ing over  a  period  of  from  one  to  three  months,  becoming 
"raw"  and  "commercially  pure"  linseed-oil,  costing  from 
55  cents  to  75  cents  per  gallon. 

"Boiled"  linseed-oil  costs  a  little  more,  and  is  produced  by 
heating  raw  oil  to  400  or  500  degrees  F.,  at  which  tempera- 
ture the  vegetable  matter  of  the  oil  is  attacked,  at  which  stage 
from  i  to  3^  of  either  litharge  or  the  red  oxide  of  lead,  some- 
times with  a  .small  quantity  of  the  oxide  of  manganese,  is 


PAINTING.  257 

added.  Raw  oil  requires  from  five  to  six  days  in  drying, 
while  the  boiled  oil  dries  in  about  one-fifth  the  time. 

No  other  known  oil  has  the  power  for  absorbing  oxygen 
that  is  possessed  by  linseed-oil,  but  in  the  process  it  has 
been  shown  by  Muelder  that  the  oil  gives  off  carbonic  acid, 
acetic  and  formic  acid,  and  possibly  water-vapors,  the  slow  es- 
cape of  which  probably  accounts  for  the  well-known  porosity 
of  the  dried  film,  and  on  account  of  which  the  film  has 
remarkable  absorbent  capacity,  acting  like  a  sponge  in  the 
presence  of  moisture,  which  Dr.  Dudley  considers  the  primary 
cause  of  the  decomposition  of  the  material,  although  not  sat- 
isfied that  the  water  itself  is  the  cause  of  the  decay. 

Like  other  vegetable  fixed  oils,  linseed-oil  contains  glycer- 
ine and  liquid  acid  fats.  According  to  many  authorities, 
these  fats  in  the  presence  of  oxides,  especially  lead,  produce 
salts  by  the  combination  of  the  acid  fats  with  the  lead  of  the 
oxide ;  saponify,  resulting  in  metallic  soaps.  Amongst 
others,  Prof.  J.  Spennrath  combats  this  theory  with  many 
valid  arguments,  amongst  which  he  asserts  that  "  if  we  should 
treat  any  soap  with  diluted  acid,  which  is  capable  of  dissolv- 
ing the  metallic  oxide  contained  therein,  it  is  decomposed, 
and  the  fatty  acid  separated.  The  latter  then  swims  in  the 
liquid.  A  dried  oil-paint  can  never  be  dissolved  by  diluted 
acid  in  this  way."  Again,  "a  weak  alkalized  liquid,  for  in- 
stance, a  one  per  cent,  soda  solution,  dissolves  after  a  pro- 
longed application  any  dried-up  oil-paint  coating.  We  then 
obtain  the  coloring  matter  what  was  used  in  an  unchanged 
condition.  A  real  soap  cannot  be  decomposed  by  a  soda 
solution." 

Prof.  Spennrath  admits,  however,  that  the  rapid  effects  of 
oxidation  produce  more  or  less  effect  upon  any  oxidizable 
pigment,  and  several  other  recognized  authorities  assume,  in 
the  case  of  at  least  one  such  pigment — the  red  oxide  of  lead — 
that  a  chemical  combination  is  produced,  analogous  to  sapon- 


258  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

ification,  but  with  also  a  cement-like  action,  the  substance 
"setting  "  into  a  compact  mass  during  a  short  space  of  time. 

Linseed-oil,  then,  alone  or  in  combination  with  some  in- 
ert pigment  or  substance,  absorbs  oxygen  rapidly  and  in  con- 
siderable quantities,  wherever  found,  at  the  same  time  throw- 
ing off  volatile  gases,  becoming  porous  and  absorptive  as  it 
hardens  into  a  tenacious,  elastic  vegetable  gum ;  while  in  so- 
lution or  combination  with  active  mineral  oxidizable  com- 
pounds, a  radical  change  takes  place,  the  resulting  substance 
"being  analogous  to  a  metallic  salt  or  soap,  but  evincing 
cement-like  properties. 

Pigments. — Of  the  elementary  substances  as  a  base  of 
paint  mixtures,  it  is  generally  conceded  that  Carbon  C,  as 
lampblack  (or  graphite),  or  the  hydrocarbon  asphaltum  has 
given  the  best  results  for  a  metallic  protective  covering,  while 
in  the  opinion  of  many  the  metallic  oxides  as  red  oxide  of 
iron,  (Fe2O3)  and  the  red  oxide  of  lead  (Pb3O4)  give  equal  or 
better  results.  These  substances  have  been  used  singly,  in 
combination  with  each  other,  or  mixed  with  some  of  the 
"inert"  pigments,  such  as  silica,  kaolin,  talc,  whiting,  gyp- 
sum, etc.  Comparisons,  endeavoring  to  show  why  certain  of 
the  many  pigments  should  not  be  used,  have  been  so  often 
made  by  eminent  scientists  that  it  will  be  the  attempt  of  the 
author  to  give  some  reasons  for  the  faith  that  is  in  him  as  to 
why  certain  of  these  bases  should  be  used  upon  metallic  struc- 
tures, such  as  stand-pipes,  not  affected  by  heat  or  by  sulphur- 
ous gases. 

Before  the  American  Society  of  Mechanical  Engineers, 
June,  1895,  Mr.  M.  P.  Wood,  a  member  of  the  society,  read 
a  paper  entitled  "  Rustless  Coatings  for  Iron  and  Steel," 
which  is  remarkably  clear  and  interesting,  and  from  which 
is  quoted  the  following: 

"Red  Oxide  of  Lead,  Pb3O4  (Minium). — This  oxide  is 
iound  native  in  various  parts  of  the  world,  mixed  with  other 


PAINTING.  259 

ores  of  lead,  and  probably  resulting  from  their  oxidation.  In 
some  localities  it  accompanies  cerusite  or  white-lead  ore. 

"  When  prepared  for  analysis,  or  when  the  commercial 
article  is  freed  from  the  protoxide  by  digestion  with  a  solu- 
tion of  acetate  of  lead,  it  contains  90.63$  of  lead  and  9.37$  of 
oxygen,  numbers  agreeing  exactly  with  the  formula  Pb3O4. 

4 '  It  may  be  regarded  either  as  a  compound  of  the  protoxide 
and  peroxide  of  lead  PbO.PbOa,  or  perhaps  of  the  protoxide 
and  sesquioxide,  PbO.Pb2O3,  analogous  to  the  magnetic 
oxide  of  iron.  Its  specific  gravity  ranges  from  8.6  to  8.94. 

*  •'  The  commercial  red  oxide  of  lead  is  formed  when  the  pro- 
toxide is  kept  at  a  low  red  heat  for  a  considerable  time  in 
contact  with  air;  also,  after  the  previous  formation  of  hy- 
drated  protoxide  and  basic  carbonate  of  lead,  when  lead  shav- 
ings are  strewn  upon  the  water,  the  vessel  being  loosely  cov- 
ered and  set  aside  for  some  months,  the  formation  of  red 
lead  taking  place  upon  the  surfaces  of  the  lead  exposed  to  the 
air.  .  .  .  Commercial  red  lead  contains  all  of  the  foreign 
metallic  oxides — such  as  the  oxides  of  silver,  copper,  and  iron 
— with  which  the  massicot  or  litharge  used  in  preparing  it  is 
contaminated.  It  is  also  adulterated  with  red  oxides  of  iron, 
boles,  or  brick-dust;  these  substances  remain  undissolved 
when  the  red  lead  is  digested  in  warm  dilute  nitric  acid ; 
boiling  hydrochloric  acid  extracts  the  sesquioxide  of  iron  from 
the  residue.  .  .  .  The  use  of  red  lead  as  a  pigment  is  pos- 
sibly of  earlier  origin  than  any  of  the  oxides  of  iron,  ochres, 
and  other  substances,  natural  or  artificial,  of  which  we  have 
any  record,  unless  it  be  asphaltum  or  lampblack.  The  many 
miscellaneous  pigments  which  have  come  forward,  been  tried, 
and  found  wanting  in  some  one  or  other  of  the  qualities  which 
constitute  a  good  paint  are  almost  numberless.  There  is  no 
other  color-pigment  whose  use  as  a  protective  covering  to 
wood,  brick,  stone,  or  metal  has  been  so  uniformly  satisfactory 
and  successful  as  red  lead,  and  any  failure  to  fulfil  its  mission 


260  TOWERS  AND    TANK'S  FOR    WATER-WORKS. 

can  be  traced  directly  to  some  agency  foreign  to  the  lead  itself, 
used  either  in  its  preparation  or  in  the  methods  of  its  applica- 
tion." 

A  paper  read  by  Prof.  A.  H.  Sabin,  before  the  Boston 
Society  of  Civil  Engineers,  November,  1899,  says  of  the  red 
oxide  of  lead  :  "  There  yet  remains  to  be  described  one  other 
important  pigment,  red  lead.  This  is  entitled  to  a  place  in  a 
class  by  itself,  because  it  is  intermediate  between  the  paints, 
which  it  resembles  in  being  used  mixed  with  oil,  and  the 
cements,  which  it  resembles  in  its  process  of  solidification.  It 
is,  in  fact,  a  powerful  basic  substance,  and  combines  chemic- 
ally with  the  oil,  forming  an  insoluble,  hard,  tenacious  mass,  in 
which  the  uncombined  particles  of  the  excess  of  red  oxide  are 
imprisoned.  This  is  what  constitutes  the  protective  film  when 
a  red-lead  paint  is  dry." 

By  some  authorities  it  is  claimed  that  in  the  chemical  com- 
bination the  glycerine,  as  well  as  the  acid  fats,  is  changed  by 
the  lead  oxide,  volatilization  of  the  glycerine  being  prevented, 
but  in  oxidizing  through  the  process  common  to  all  linseed- 
oils,  the  mass  is  rendered  insoluble,  elastic,  and  adhesive ;  but 
it  seems  very  probable  that  the  glycerine,  not  being  a  stable 
product,  soluble  in  water  and  volatilized  by  heat,  acts  as 
described  by  Muelder,  the  film  being  rendered  more  or  less 
porous  by  the  escape  of  the  gases. 

Litharge  mixed  with  commercial  glycerine  to  a  pasty 
mass  takes  a  most  hard  and  tenaceous  "set"  when  exposed 
to  the  action  of  the  atmosphere  for  twenty  to  thirty  minutes. 

It  is  stated  by  Wood  that,  during  the  process  of  setting, 
red  lead  and  oil  will  oxidize  the  surface  of  clean  iron  or  steel, 
forming  the  black  oxide  of  iron  which  is  non-corrosive.  It  is 
also  believed  to  be  a  fact  that  where  moisture  exists  upon  the 
metallic  surface,  the  oil  and  lead  rapidly  absorbs  this  in  the 
chemical  change  requiring  oxygen  wherever  found. 

These  estimable  qualities,  however,  are  offset  to  a  certain 


PAINTING,  26l 

extent  by  the  well-established  facts  that,  on  account  of  its 
specific  gravity  being  far  in  excess  of  that  of  the  oil,  when 
mixed  and  spread  upon  perpendicular  surfaces,  the  paint 
41  runs"  or  "sags,"  the  pigment  separating  from  the  oil,  the 
coat  producing  a  streaked  appearance  and  not  affording  an 
even  covering,  and  it  would  therefore  seem  that  its  use  should 
be  confined  to  metallic  plates  and  shapes  before  assembling 
and  where  the  coating  can  be  applied  while  the  member  is 
horizontal  or  nearly  so. 

Again,  owing  to  the  rapidity  of  oxidation,  the  red  lead  and 
oil  sets  so  quickly  that  it  is  of  difficult  application,  but  this 
objection  can  be  partly  overcome  by  an  addition  of  a  carbon- 
pigment,  such  as  lampblack,  which  is  an  impalpable  powder, 
practically  indestructible,  in  a  measure  elastic,  with  the 
power  of  repelling  moisture,  and  itself  one  of  the  best-known 
preservatives  of  metals,  but  comparatively  useless  when  applied 
alone,  from  a  fault  in  an  opposite  direction;  that  is,  it  takes  too 
long  to  dry. 

In  conjunction,  these  two  pigments  modify  the  opposite 
objectionable  properties  of  each,  while  the  fine  carbon-pow- 
der assists  in  filling  any  voids  in  the  mass,  due  to  imperfect 
combination. 

In  the  manufacture  of  such  paint  it  is  a  prime  necessity 
that,  to  produce  satisfactory  results,  each  ingredient  should  be 
chemically  pure,  and  the  degree  of  purity  will  determine  the 
relative  efficiency.  Suitable  proportions  have  been  found  in 
20  pounds  of  red  lead,  I  pound  of  carbon  as  lampblack  to 
5  or  6  pounds  of  raw  linseed-oil.  The  bulk  will  be  about  i 
gallon,  with  a  covering  capacity  of  about  50  square  yards  of 
surface  for  the  first  coat,  the  film  being  approximately  .002 
of  an  inch  in  thickness.  The  cost  will  be  about  $1.50,  and 
the  amount  paid  for  labor  in  spreading  will  run  about  5  cents 
per  square  yard  where  the  services  of  an  experienced  painter 
are  employed. 


262  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

While  the  preponderence  of  evidence  is  in  favor  of  the  use 
of  red  lead  in  oil  for  protective  coatings  for  iron  and  steel, 
numerous  failures  are  recorded,  but  as  a  comparison  of  evi- 
dence might  be  continued  ad  infinitum,  such  a  task  will  not 
be  attempted  here,  further  than  to  mention  the  results  of  a 
series  of  tests,  extending  over  two  years,  and  made  by  Prof. 
Sabin  upon  steel  plates  coated  with  a  wide  variety  of  paint 
covering,  the  samples  being  afterwards  immersed  continuously 
and  subject  for  two  years  to  the  action  of  both  salt  and  fresh 
waters.  Prof.  Sabin's  conclusions,  represented  in  a  paper 
read  before  the  Engineers'  Club  of  Philadelphia,  May, 
1900,  were  that  "  the  character  of  the  pigment  in  a  majority 
of  cases  made  very  little  difference :  that  oil-paints  did  not 
withstand  the  action  of  the  water  as  well  as  varnish-paints," 
but  that  "  red  lead  stood  better  than  any  of  the  oil-paints. 
There  is  no  question  about  it.  It  did  not  stand  as  well  as 
many  varnish  paints.  It  did  not  stand  as  well  as  some  var- 
nishes without  any  pigment  in  them." 

Structures  are  not  as  a  rule  subject  to  such  action  of  the 
water  as  took  place  in  Prof.  Sabin's  experiments,  and  while 
these  were  very  carefully  made  and  recorded,  certain  results 
where  metal  plates  were  submerged  would  not  necessarily 
have  a  distinct  bearing  where  a  structure  is  subject  only  to 
atmospheric  influence ;  but  in  view  of  the  fact  that  such  struc- 
tures as  tanks,  intermittently  or  continuously  rilled  with  water, 
are  the  prime  subject  of  consideration  here,  his  experiments 
are  of  considerable  value. 

Asphaltic  Varnish. — Varnish  differs  from  paint  only  in 
the  base — the  medium,  linseed-oil,  remaining  the  same.  In 
varnish,  the  pigment  gives  place  to  various  resins,  dissolved  ia 
the  spirits  of  turpentine,  a  volatile  oil.  These  resins  are  of 
vegetable  origin,  and  are  classed  as  "  recent  resins,"  the  resin- 
ous gum  of  a  recent  period,  and  "  fossil  resins,"  the  volatilized 
gums  of  trees  long  buried  in  the  earth.  Varnish  resins  are 


PAINTING.  263 

largely  found  in  Africa,  South  America,  New  Zealand,  and  the 
East  Indies.  The  general  process  of  varnish  manufacture  is 
the  heating,  in  a  suitable  receptacle,  of  the  resins  to  from  600 
to  800  degrees  F.,  at  which  point  the  resins  melt,  being  de- 
composed by  the  heat. 

At  this  point,  hot  linseed-oil  is  added,  and  the  contents 
stirred  until  fully  combined ;  after  cooling,  the  mixture  is 
dissolved  or  diluted  with  spirits  of  turpentine,  to  permit  the 
proper  flow  of  the  varnish  under  the  brush.  The  greater 
amount  of  oil  used,  the  greater  the  elasticity,  tenacity,  and 
toughness,  and  the  less  brittleness,  which  are  desirable  quali- 
ties where  the  varnish  coat  is  subject  to  mechanical  injury. 
In  addition  to  the  vegetable  resins,  a  "  mineral  resin,"  as  it 
has  been  called,  or  asphaltum,  is  often  used.  Its  oil,  by  dry 
distillation,  is  of  a  yellow  color,  and  said  to  resemble  closely 
the  oil  of  amber.  Used  in  considerable  quantities  in  the  manu- 
facture of  varnish,  it  exhibits  remarkable  non-drying  qualities, 
but  its  compensating  advantages  are  its  cheapness,  elasticity, 
tenacity,  durability,  and  insolubility. 

Prof.  Sabin  gives  the  following  why  varnish  is  better 
than  oil:  "The  reason  why  varnish  is  better  than  oil  is 
that  it  is  more  durable,  smoother,  and  more  brilliant,  and 
because  the  resin  dissolving  in  the  oil  makes  it  harder;  it 
makes  a  film  that  is  harder,  and  still  retains  a  high  degree  of 
elasticity — not  somuch  elasticity,  perhaps,  as  theoriginal  alone, 
but  a  very  high  degree  of  elasticity ;  and  it  is  very  much  more 
impervious  to  moisture  than  oil." 

From  a  paper  read  June,  1895,  by  Prof.  A.  H.  Sabin,  be- 
fore the  American  Society  of  Civil  Engineers,  the  following 
is  quoted  : 

"  It  has  long  been  known  to  varnish-makers  that  the  fossil 
resins  known  as  copals,  such  as  the  New  Zealand  kauri,  when 
added  to  asphalt-varnishes,  improve  their  durability.  This 
is  probably  partly  owing  to  the  fact  that  such  compounds  are 


264  TOWERS  AND    TANKS  FOR    WATER- WORKS. 

of  greater  density,  as  the  resin  dissolved  in  the  oil  and  asphalt 
tends  to  make  a  more  compact  substance,  and  partly  because 
it  increases  its  electric  insulating  power,  also  in  consider- 
able measure  because  such  a  resin  is  very  indifferent  to  the 
action  of  sulphur-gases.  For  all  these  reasons  it  seems  to  the 
writer  that  the  maximum  of  durability  is  only  to  be  reached 
by  a  compound  of  hard  asphaltum,  copal-gum,  and  linseed- 
oil,  thinned,  if  necessary,  with  pure  turpentine.  It  is  of  the 
highest  importance  that  the  oil  employed  should  be  so  refined 
as  to  have  its  non-drying  constituents  removed,  so  as  to  avoid 
as  much  as  possible  the  use  of  dryers.  This  is  of  more  im- 
portance than  in  a  pigment  and  oil-paint,  because  the  most 
obvious  thing  about  asphalt  is  mentioned  in  the  observations 
of  M.  Riffault,  made  some  thirty  or  forty  years  ago,  that 
'  asphalt  destroys  the  drying  quality  of  oil.'  ' 

This  is  due  to  the  fact  that,  being  a  viscous  substance,  it 
closes  the  pores  of  the  oil  and  thus  obstructs  the  entrance  of 
air  and  moisture,  which  is  also  the  cause  of  the  great  dura- 
bility of  such  compounds. 

Not  only  is  it  necessary  to  have  the  most  suitable  materi- 
als in  such  proportions  as  experience  has  shown  to  be  best, 
but  the  ingredients  should  be  compounded  in  the  most 
approved  manner. 

Long  experience  has  shown  that  there  are  certain  tempera- 
ture-curves to  be  followed  in  combining  certain  materials, 
differing  for  different  compounds,  a  departure  from  which  in- 
jures the  durability  of  the  resultant  compound.  The  upper  parts 
of  the  curves  approach  dangerously  near  to  the  decomposing 
point  of  the  oil,  and  it  has  been  found  that  a  suitably  refined 
pure  oil  has  that  point  more  than  100  deg.  F.  higher  than 
common  oil;  it  is  on  this  account,  also,  important  to  use  the 
highest  skill  in  the  manufacture.  The  choice  of  ingredients 
is  of  less  importance  than  their  proper  proportion,  and  this 
again  is  of  no  more  value  than  the  use  of  the  best  process 


PAINTING.  265 

of  combination.  Against  the  use  of  varnishes  upon  metallic 
surfaces,  it  has  long  been  pointed  out  that,  on  account  of  the 
volatile  properties  of  the  medium,  either  turpentine  or  ben- 
zine, its  rapid  evaporation  causes  a  fall  of  temperature, 
causing  a  deposition  of  moisture  upon  the  surface,  which 
acts  deleteriously  upon  the  resin  or  gum  of  the  varnish,  while 
preventing  the  proper  adhesion  of  the  film  to  the  metal,  and 
possibly  causing  the  commencement  of  the  corrosive  action 
of  moisture  upon  the  metallic  surface. 

The  cost  of  a  well-prepared  asphaltic  varnish,  of  pure  ma- 
terials, will  be  about  $1.50  per  gallon,  which  will  cover  about 
40  sq.  yds.  of  surface,  one  coat. 

Application. — It  is  generally  conceded  that  two  coats  of 
good  paint  will  last  at  least  three  times  as  long  as  one  coat/ 
and  that  the  first,  or  priming  coat,  is  of  especial  importance. 

In  the  prize  essay  of  Prof.  Spennrath,  Director  of  the 
Technical  School  at  Aix-la-Chapelle,  upon  "Protective  Cover- 
ings for  Iron,"  his  conclusions  are  that:  "It  is  therefore 
advisable,  in  putting  on  iron  coatings,  to  prime  with  a  paint  as 
heavy  as  possible  and  have  the  upper  coat  rich  in  oil."  The 
specific  gravity  of  red  lead  being  shown  to  be  about  9.0,  it 
is  the  heaviest  known  pigment  in  use  in  the  preparation  of 
paints. 

In  a  number  of  exhaustive  tests,  Prof.  Spennrath  distinctly 
traces  the  bad  experiences  with  red-lead  coatings  to  the  action 
of  heat,  under  which  conditions  the  metal  expands,  the  paint- 
skin  remaining  hard  and  brittle,  a  severe  stretching  takes  place, 
cracks  and  rents  develop  in  the  paint-coating,  and  as  a  conse- 
quence rust  appears.  Where  the  atmosphere  contains  hydric 
sulphide,  the  red  lead  is  changed  to  the  sulphide  of  lead,  ac- 
cording to  Prof.  Spennrath,  to  which  he  attributes  the  sole 
specific  weakness  of  red  lead  as  a  pigment. 

To  sum  up,  in  favor  of  the  use  of  red  lead  and  oil  is  its 
well-known  high  specific  gravity  and  its  peculiar  chemical 


266  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

property  of  combination,  resulting  in  the  production  of  a 
coating  or  film  of  a  particularly  tenacious,  hard,  and  insoluble 
character,  when  not  subject  to  great  heat  or  sulphurous  gases, 
which  is  seldom  to  be  considered  in  connection  with  such 
structures  as  towers  and  tanks.  The  red-lead  paint,  however, 
lacks  elasticity,  resulting  in  the  formation  of  air-cracks,  and 
its  porosity  from  the  escape  of  volatile  gases  during  the  proc- 
ess of  hardening  seems  to  be  well  established.  Moreover,  its 
high  specific  gravity  has  the  disadvantage  of  causing  the  pigs 
ment  to  "sag"  or  run  away  from  the  oil  when  being  applied, 
resulting  in  streaking  or  imperfect  and  uneven  covering, 
while  its  quick-setting  qualities  render  this  paint  unsatisfac^ 
tory  and  difficult  to  handle.  This  last  tendency  may  be  in 
part  or  entirely  removed  by  the  addition  to  the  mixture  of 
carbon,  usually  in  the  form  of  lampblack,  which  further  aids, 
as  has  been  shown,  in  diminishing  the  porosity  offered  as  an 
objection  to  the  use  of  lead  and  oil,  while  if  the  paint  is  used, 
as  before  erection,  upon  materials  and  surfaces  which  may  be 
placed  horizontally  or  nearly  so,  the  pigment  has  little  or  no 
opportunity  to  settle  out  of  the  oil  or  "  sag." 

For  all  the  reasons  submitted,  it  would  appear  that  as  a 
priming  coat,  or  first  coat,  red  lead,  lampblack,  and  linseed- 
oil,  when  applied  upon  iron  or  steel  surfaces  of  structural  ma- 
terial before  erection,  affords  the  best  known  protection  to 
metallic  corrosion ;  it  is  also  a  well-established  fact  that  red 
lead,  usually  as  a  red-lead  paste,  is  used  in  water  and  steam- 
pipe  fitting  to  produce  a  close  and  perfect  joint,  and  that 
when  applied  upon  the  laps  of  steel  plate  intended  to  be  used 
in  water-tank  construction,  the  same  tendency  toward  pro- 
ducing a  water-tight  joint  is  observed,  and  the  use  of  this 
material  for  such  purposes  minimizes  the  most  objectionable 
practice  of  making  it  necessary  to  resort  to  a  natural  or  rust- 
joint  to  secure  the  necessary  degree  of  tightness  between  the 
metal  plates. 


PAINTING.  267 

It  also  seems  equally  sure  that  suitable  finishing  coats 
should  be  provided  and  applied  over  the  priming  coat,  and 
that  this  last  film  should  be  of  small  specific  gravity,  elastic, 
impervious  to  moisture,  hard,  and  tenacious;  it  should  be  in- 
different to  sulphurous  gases  and  electrically  insulating,  all  of 
which  properties  seem  to  be  fulfilled  to  a  greater  degree  by 
an  asphaltic  varnish  than  any  known  varnish  or  paint  compo- 
sition. On  account  of  its  ease  of  application  and  quick-dry- 
ing powers,  it  is  particularly  suitable  for  application  upon 
structures  being  erected  in  the  open  air  and  exposed  to  the 
weather,  while  the  characteristic  of  a  volatile  composition  to 
produce  a  deposition  of  moisture  is  of  no  consequence  when 
that  moisture  is  not  formed  upon  the  metal  itself,  but  upon  a 
cement-like  coating,  which,  besides,  has  a  power  for  decom- 
posing moisture  by  the  absorption  of  its  oxygen. 

Either  paint  or  varnish  coats  should,  when  possible,  be 
put  on  under  the  most  favorable  atmospheric  conditions,  the 
best  season  being  during  the  autumn,  when  the  temperature  is 
apt  to  remain  more  uniform,  and  when  fogs  and  rains  are  less 
likely  to  occur.  A  suitable  interval  of  time  should  be  ob- 
served in  order  that  the  first  coat  should  be  entirely  and 
completely  dry  before  the  second  coat  is  added.  In  order  to 
have  the  painter  or  contractor  observe  this,  and  to  make 
sure  that  more  than  one  coat  is  put  on,  the  several  coats 
should  differ  slightly  in  color,  so  that  such  neglect  would  be 
readily  determined  and  corrected. 

In  the  purchase  of  materials,  the  preference  should  be 
given  old  and  long-established  houses,  whose  reputation  for 
quality  is  well  known,  and  it  should  not  be  expected  that  the 
purchase  of  paint  materials  at  less  than  market  prices  will  be 
conducive  of  anything  but  the  practice  of  adulterating  the 
products. 

In  the  application  of  the  paints,  which  should  have  been 
selected  with  considerable  care,  only  experienced  and  reliable 


268  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

mechanics  should  be  employed ;  in  the  long  run,  besides  their 
ability  to  spread  a  smooth  and  regular  coat,  their  experience 
will  save  sufficient  materia',  or  make  the  same  material  go 
enough  further,  to  warrant  the  employment  of  the  skilled  me- 
chanic, if  the  selection  of  the  individual  is  put  upon  a  basis 
of  first  cost,  rather  than  of  comparative  excellence. 

Repainting. — Intelligent  and  systematic  care  should  be 
given  a  structure  continuously  after  painting,  remembering 
that  "an  ounce  of  prevention  is  worth  a  pound  of  cure." 
Repainting  should  not  be  too  long  delayed,  and  at  the  first 
evidence  of  this  necessity,  the  old  paint  should  be  carefully 
removed  before  the  fresh  covering  is  applied.  In  doing  this, 
a  strong  caustic  solution  should  be  used  to  partially  decom- 
pose the  old  film,  and  steel  scrapers  and  wire  brushes  then 
employed  to  detach  the  coat.  Immediately  afterward,  the 
metallic  surface  should  be  carefully  washed  down  with  water 
and  dried,  any  deep-seated  rust-spots  or  paint  which  it  has 
been  impossible  to  remove  otherwise  being  burned  away  by 
the  application  of  the  flame  from  a  painter's  torch. 

It  stands  to  reason  that  the  more  care  exercised  in  clean- 
ing down  to  the  metal,  the  better  the  results  from  the  new 
paint  coating  to  be  applied,  and  the  greater  logevity  of  the 
metal. 

In  view  of  the  constantly  widening  range  of  the  use  of  steel 
for  structural  purposes,  it  is  not  surprising  that  constant  effort 
should  be  directed  toward  determining  the  best  protective  coating 
for  iron  and  steel.  At  a  recent  meeting  of  the  Am.  Soc.  for  Test- 
ing Materials,  a  committee  report  of  much  importance,  presented 
by  its  chairman,  Mr.  S.  S.  Voorhees,  is  as  follows: 

''•  PROTECTIVE    COATINGS    FOR    IRON    AND    STEEL. 

"  The  membership  of  the  committee  has  been  increased  from 
the  original  6  to  17  members,  and  the  committee  has  aimed  to 


PAINTING.  269 

include   representatives   of  every   class   engaged   in   commercial 
production  of  protective  coatings. 

"  The  three  meetings  of  the  committee  held  during  the  year 
have  so  far  been  confined  to  discussing  the  best  methods  of  ob- 
taining the  desired  data  for  a  comprehensive  report  on  this  sub- 
ject. 

"  Before  beginning  this  work  it  was  considered  necessary  to 
put  in  concrete  form  several  working  headings: 

"  i.  Requirements  for  a  satisfactory  protective  metal  coating* 

"  2.  Methods  used  and  suggested  to  determine  if  the  protec- 
tive coating  is  efficient. 

"  3.  An  index,  with  abstracts,  if  possible,  of  general  and 
current  literature  bearing  on  this  subject,  which  has  appeared  in 
English,  French,  German,  and  American  publications. 

"  4.  A  classified  list  of  all  coatings  used  or  suggested  for  the 
protection  of  iron  and  steel. 

"  Sub-committees  on  the  first  two  subjects  have  submitted 
reports;  sub-committees  on  the  last  two  subjects  report  progress 
and  request  further  time  for  final  report. 

"  The  report  of  the  sub-committee  on  requirements  for  a  satis- 
factory protective  metal  coating  resulted  in  the  following  recom- 
mendations : 

"  IN  PREPARATION  OF  SURFACE  FOR  PAINTING  it  is  considered 
necessary  that  surface  be  free  from  grease  and  dirt,  and  that 
all  detachable  mill  scale  and  rust  be  removed.  Material  which 
cannot  be  removed  by  hammer  and  chisel  or  wire  brush,  it  is 
thought,  will  not  affect  the  durability  of  the  coating.  The  use 
of  the  sand-blast  is  recommended,  provided  it  is  the  opinion  of 
the  engineer  that  the  cost  is  warranted,  but  it  is  not  considered 
necessary  in  all  cases. 

"  APPLICATION  OF  THE  PAINT. — It  is  recommended  that  the 
successive  paint  coatings  should  be  as  thick  as  possible,  com- 
patible with  satisfactory  spreading  with  the  brush  or  machine. 
The  brush  marks  should  flow  out.  The  paint  should  not  con- 


27O  TOWERS  AND    TANKS   FOR    WATER-WORKS. 

tain  any  large  amounts  of  volatile  matter,  so  as  to  chill  the  surface 
by  evaporation. 

"  DRYING. — It  does  not  seem  possible  without  further  ex- 
perimentation to  reach  a  final  conclusion  on  this  point.  Whether 
the  paint  coats  shall  dry  in  six  or  twenty-four  hours  is  a  matter 
to  be  determined  by  the  contingencies  of  the  case.  In  general 
this  recommended  that  as  much  time  as  possible  be  allowed 
between  coats.  It  is,  however,  considered  practicable  to  have 
an  efficient  metal  coating  dry  in  eight  hours. 

"  SUCCESSIVE  COATINGS. — The  under  coatings  must  not  be 
softened  or  acted  upon  by  the  subsequent  coats  of  paint. 

"  PROTECTIVE  POWER. — This  is  the  keystone  of  the  whole 
subject.  The  coating  must  protect.  To  accomplish  this  it  is 
recommended  that  the  coating  must  have  the  maximum  imper- 
meability to  moisture,  air,  and  carbon  dioxide.  Iron  and  steel 
will  not  rust  in  dry  air  or  in  water  free  from  air  and  carbon  dioxide. 
The  best  protection  will,  therefore,  be  obtained  from  the  most 
impervious  coating.  To  this  end  the  pigment  should  be  as  finely 
ground  as  possible;  and,  finally,  it  is  recommended  that  the 
vehicle  or  pigment,  or  both,  be  water  repellent.  Whether  this 
last  characteristic  is  to  be  obtained  by  a  pigment  such  as  lamp- 
black, or  by  the  use  of  some  non-drying  oi ,  must  be  the  subject 
for  further  investigation. 

"  DURABILITY. — It  is  the  opinion  of  the  committee  that  coat- 
ings should  be  efficient  under  ordinary  conditions  for  at  least 
five  years.  The  durability  measures  the  life  of  the  coating; 
it  should  therefore  adhere  to  the  metal  through  all  ranges  of  con- 
traction and  expansion  without  peeling  or  cracking. 

"  Neither  the  pigment  nor  the  vehicle,  nor  compounds  resulting 
from  a  reaction  of  the  two,  should  cause  a  disintegration  of  the 
coating. 

"It  is  further  recommended  that  the  coating  should  not  be 
affected  by  products  necessary  for  the  maintenance,  equipment, 
or  use  of  the  structure  protected.  This  applies  especially  to  the 


PAINTING.  271 

softening  of  paint  on  bridges  by  burning  and  lubricating  oils 
from  passing  trains. 

"  It  is  finally  recommended  that  the  coating  be  of  such  a  char- 
acter as  to  successfully  resist  the  mechanical  injury  due  to  sand, 
cinders,  and  other  material  carried  by  the  wind. 

"  FEASIBILITY  OF  RECOATING. — There  can  be  no  question 
that  a  satisfactory  coating  must  permit  recoating  when  needed 
without  additional  labor  for  cleaning  and  removing  old  coat. 

"  COST. — Upon  this  point  it  is  only  necessary  to  say  that  the 
other  valuable  requirements  being  obtained,  that  coating  is  best 
which  can  be  furnished  and  applied  at  minimum  cost. 


"  SUB- COMMITTEE      ON      TESTS     TO     DETERMINE      EFFICIENCY     OF 

COATING. 

"It  is  the  opinion  of  your  committee  that  it  is  useless  to  pre- 
scribe the  same  tests  to  all  classes  of  protective  coverings.  An 
efficient  coating  in  the  dry  atmosphere  of  the  Western  States 
may  fail  to  withstand  the  moist  saline  air  of  the  coasts.  A  coat- 
ing which  is  perfect  for  structural  steel  under  a  static  load  may 
fail  entirely  when  subjected  to  vibratory  shock  imposed  on  bridge 
members  and  steel  cars.  In  short,  tests  must  be  in  harmony 
with  conditions  imposed  in  service. 

"  The  general  cause  of  failure  of  coatings  to  protect  is  the  same 
as  the  corrosion  of  the  metal  itself,  i.e.,  moist  air  and  carbon 
'dioxide.  Dilute  acids,  as  a  rule,  have  far  less  action  on  paint 
films  than  alkaline  solutions.  A  paint  made  from  some  inert 
pigment  and  linseed  oil  will  show  no  sign  of  disintegration  when 
immersed  for  days  in  a  dilute  sulphuric-acid  solution  which  would 
rapidly  dissolve  the  metal  it  protected,  and  the  same  paint  would 
go  to  pieces  in  a  few  hours  when  exposed  to  the  action  of  a  corre- 
spondingly strong  solution  of  ammonia  or  carbonate  or  caustic 
alkalies.  Strong  acid  solutions  rapidly  destroy  the  coating, 


272  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

but  it  is  rare  that  such  conditions  exist,  and,  if  necessary,  can 
be  met  by  special  requirements. 

"It  is  recommended  that  tests  be  adapted  to  the  demands 
of  service  conditions  and  divided  into  three  broad  classes: 

"  i."  Actual  service  tests,  under  normal  conditions,  applied  to 
structure  to  be  protected. 

"  2.  Accelerated  tests,  applied  to  specially  prepared  surfaces, 
and  subjected  to  abnormally  severe  conditions. 

"  3.  Chemical  tests  to  determine  the  constituents  and  adultera- 
tions of  the  pigment  and  vehicle,  as  far  as  the  knowledge  of  the 
.subject  will  admit. 

"It  is  undoubtedly  true  that  the  first  set  of  tests  gives  the  de- 
sired information  in  a  most  conclusive  manner,  but,  unfortunately, 
the  truth  comes  too  late  to  remedy  the  evil  if  the  protection  is 
insufficient  to  prevent  corrosion. 

"It  is  further  considered  that  the  function  of  this  committee 
is  not  to  specify  any  covering  or  coverings  as  protective,  but  to 
specify  tests  which  coatings  must  stand  to  assure  maximum 
efficiency.  It  will  therefore  be  necessary  to  work  along  the 
lines  of  accelerated  and  chemical  tests,  selecting  those  which 
harmonize  with  the  results  of  long-time  service  experiments, 
and  ultimately  formulating  laboratory  tests  which  can  be  relied 
upon  to  give  the  desired  information. 

"  It  should,  however,  be  realized  that  in  this  work  chemical 
analysis  must  be  used  to  supplement  experience,  not  to  provide 
it.  In  general,  it  is  known  by  previous  experiments  that  certain 
pigments  and  oils  give  durability  and  protection,  while  others 
fail  in  these  essentials ;  but  it  will  not  do  to  condemn  the  unknown 
without  the  aid  of  experience. 

"  A  review  of  the  suggested  accelerated  tests  shows  a  variety 
of  methods  to  impose  abnormally  severe  conditions.  These 
tests  have  in  some  cases  little  connection  to  service  requirements, 
but  it  is  believed  that  the  results  obtained  by  the  methods  selected 
will  be  in  harmony  with  long-time  service  tests. 


PAINTING.  273 

"It  is  expected  that  the  following  series  of  experiments  can 
be  conducted  through  the  cooperation  of  railroads  and  consumers 
on  one  hand,  and  the  manufacturers  of  standard  coatings  on 
the  other,  the  former  to  provide  the  structure  and  labor  and 
the  latter  the  material  to  be  applied: 

"It  is  recommended  that  two  coats  of  the  protective  coating 
be  applied  to  parts  of  full-sized  structures,  not  less  than  one 
span  of  a  bridge,  one  steel  freight-car,  or,  in  general,  one  unit 
of  dimensions  corresponding  to  above,  the  surface  to  be  pre- 
pared and  coating  to  be  applied  as  recommended  under  those 
headings. 

"At  the  same  time,  panels  of  tank  steel  2oX24Xi  in.  are 
prepared  and  coated  in  the  same  manner  as  the  structure  and 
with  the  same  batch  of  coating.  The  panels  are  coated  on  both 
sides  and  on  edges  of  sheet.  The  work  to  be  done  indoors  under 
favorable  conditions  for  drying. 

"  The  panels  are  to  have  a  J-in.  hole  bored  in  middle  of  upper 
end  to  facilitate  hanging,  and  are  to  be  stamped  with  serial  number 
on  both  sides  in  upper  left-hand  corner. 

"  Panels  are  prepared  as  above  in  pairs,  one  to  be  exposed 
i green'  and  the  other  to  be  thoroughly  dried  under  favorable 
conditions  before  testing.  The  corresponding  pair  of  'green' 
and  dry  panels  are  exposed  under  the  roofs  of  train  sheds,  in 
roundhouses  directly  over  smoke-stacks  of  engines,  from  trusses 
of  bridges,  on  roofs  of  train  sheds,  roundhouses,  and  on  roofs 
adjoining  power-house  stacks,  etc.,  in  tunnels,  on  docks  in  salt 
water  and  tidal  rivers,  where  they  will  be  immersed  twice  every 
twenty-four  hours  in  salt  and  fresh  water  in  the  ebb  and  flow 
of  tides. 

In  addition  to  above  series  of  field  panels,  special  laboratory- 
panels  on  glass  and  tank  steel  are  prepared  in  the  same  manner 
as  the  foregoing.  The  steel  panels  are  exposed  to  the  action 
of  exhaust  steam  at  a  temperature  not  to  exceed  150°  F.  foi 


274  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

twelve  hours  each  day,  and  ordinary  atmospheric  air  for  the 
remaining  twelve  hours,  the  test  to  be  continued  for  thirty  days. 

"  The  porosity  is  determined  by  noting  the  absorption  of  a 
drop  of  oil  on  the  coating.  If  the  film  is  impervious,  the  drop 
of  oil  will  run  down  the  panel  in  a  narrow  band  the  width  of  the 
original  drop,  but  if  the  life  of  the  coating  has  been  destroyed 
the  drop  of  oil  will  spread  out  to  a  more  or  less  greasy  blotch, 
depending  on  extent  of  disintegration. 

"  The  glass  panels  are  tested  for  water-repellent  properties 
by  treating  the  dried  coating  with  a  few  drops  of  water.  Evap- 
oration is  prevented  by  means  of  a  cover-glass,  and  the  coating 
examined  after  the  water  has  been  in  contact  for  twelve  hours. 

"  The  capacity  of  the  coating  to  withstand  destructive  agencies 
necessary  to  equipment  and  maintenance  of  structure  will  require 
special  tests. 

"  For  steel  cars  and  bridges  the  coating  on  glass  is  tested  with 
lubricating  and  burning  oils  to  determine  if  it  is  disintegrated. 
For  refrigerating-cars  it  is  tested  in  the  same  manner  with  a 
common  salt  solution. 

"  A  further  set  of  laboratory  tests  are  made  by  coating  saucers 
of  sheet  iron  8  inches  diameter  i  inch  deep  with  two  coats  of 
paint.  These  saucers  are  filled  with  ordinary  tap  water  and 
allowed  to  evaporate  under  cover  to  dryness,  the  water  renewed 
until  definite  conclusions  can  be  deduced. 

"  Chemical  analyses  of  the  coatings  will  also  be  made  to  deter- 
mine percentage  of  pigment,  oil,  and  volatile  matter,  with  com- 
position and  quality  of  each. 

"  The  above  service  and  laboratory  tests  are  to  be  conducted 
at  as  widely  distant  points  and  under  as  different  conditions  as 
possible.  The  service  tests  are  to  be  carefully  examined  at 
stated  intervals  and  the  entire  series  of  experiments  accurately 
tabulated  for  comparsion  with  the  long-time  service  tests. 

"  From  these  data  it  is  expected  that  laboratory  tests  can  be 


PAINTING. 


275 


formulated  which,  when  met,  will  insure  a  satisfactory  prokcthe 
metal  coating." 

The  quantity  of  any  paint  to  cover  a  given  surface  will  depend 
upon  the  smoothness,  absorption  of  the  surface  and  also  upon 
the  fluidity  of  the  mixture. 

A  finely  ground  pigment  with  linseed-oil  as  a  medium  will 
ordinarily  cover  about  600  square  feet  one-coat  or  350  square 
feet  of  two-coat  work.  A  capable  painter  should,  during  a 
day  of  eight  hours,  spread  about  800  square  feet  of  flat  surface 
and  about  half  as  much  over  structural  work.  The  latter  will 
average  for  light  work  about  250  square  feet  per  ton  of  metal. 
$2.50  per  day  may  be  taken  as  fair  wages  for  a  competent  painter. 

The  following  gives  the 

AVERAGE  SURFACE  COVERED  PER  GALLON  OF  PAINT. 


Character. 

Volume 
of 
Oil. 

Lbs. 
of  Pig- 
ment. 

Volume 
and  Weight 
of  Paint. 

Sq.  Ft. 

i  Coat. 

2  Coats. 

Cost 
per  Gal. 
Mixed. 

Red  lead  (powdered).  .  . 
Graphite  (in  oil) 

i  gal. 
I     '  ' 

22.40 

12.  ?O 

Gals.      Pounds. 
I.  4.  ..30.  40 
20        2O  50 

630 
360 

375 
21  s 

$l  .50 
I    OO 

Black  asphalt 

I     " 

17.21; 

4.0  .  .  30  oo 

ci  c 

2IO 

o  oo 

Asphaltic  varnish    . 

I     " 

i  .  o  .  .  .  8  .  oo 

4.00 

700 

I     ^O 

Pure  linseed-oil  ...... 

I     " 

87? 

o  ^o 

CHAPTER  XII. 
SHOP -PRACTICE   AND   ERECTION. 

Laying  Out  Work. — As  soon  as  the  metal  sheets  or 
plates  for  tank  or  stand-pipe  work  are  received  at  the  shop, 
they  should  be  immediately  and  carefully  unloaded  and 
stored  awaiting  the  earliest  moment  when  they  may  be 
"  laid  out."  This  process  consists  in  marking  off  the  plates 
for  shearing,  machining,  punching,  and  rolling. 

The  object  of  shearing  or  machining  is  to  put  a  bevel- 
edge  upon  the  opposite  face  of  the  plate  where  two  plates  are 
to  be  in  contact,  and  in  order  that  the  thin  edge  so  formed 
may  be  properly  and  easily  calked  after  riveting  and  that  a 
water-tight  joint  may  thus  be  secured. 

For  the  reason  that  such  work  upon  heavy  plates  has 
been  shown  to  exert  a  force  tending  to  change  the  molecular 
arrangement  of  the  metal,  this  shearing  of  plates  is  usually 
not  permitted  upon  plates  that  are  thicker  than  f  of  an  inch, 
all  plates  above  that  thickness  being  planed  to  a  bevel  by  a 
machine. 

In  laying  out,  the  rivet-hole  spacing  is  indicated  by  mark- 
ing with  a  sharp-pointed  cold-chisel,  the  widths  from  centre 
to  centre,  or  the  pitch,  having  first  been  calculated  as  has 
been  described  and  explained. 

Realizing  that  a  greater  comparative  efficiency  of  joint- 
strength  may  be  secured,  with  fewer  rivets  and  wider  spac- 
ing, where  the  largest  possible  rivet  is  used,  this  inclination 
is  sometimes  stretched  to  the  limit,  the  requirement  for  tight- 

276 


. 


SHOP-PRACTICE   AND  ERECTION.  2/7 

ness  of  joints,  as  in  stand-pipe  work,  being  considered  as 
having  been  provided  for  in  the  natural  tendency  of  such 
joints  to  close  by  rusting  after  erection,  and  to  what  extent 
this  practice  is  considered  legitimate  may  be  inferred  from 
the  following,  taken  from  an  article  on  painting,  and  from 
Prof.  Pence's  work,  "Stand-pipe  Accidents  and.  Failures  ": 
"  The  methods  of  painting  stand-pipes  are  subject  to  as  much 
variation  as  in  other  exposed  structural  metal-work.  Some 
require  that  the  inaccessible  surfaces  shall  receive  two  coats 
of  red  lead,  while  others  allow  the  omission  of  paint  from  the 
faying  surfaces  of  the  seams  to  permit  the  joints  to  rust." 

Again,  according  to  recognized  authorities,  in  forging  a 
rivet,  the  color,  indicating  its  temperature,  should  be  about 
an  orange  red,  and  with  steel  rivets,  with  a  tendency  to  rapid 
cooling,  at  this  temperature  the  larger  rivets,  especially 
hand-driven,  are  so  cold  and  tough  before  they  are  driven 
completely  home  and  the  head  forged,  that  it  is  difficult  to 
insure  a  perfect  filling  of  the  rivet-holes,  and  the  requisite 
closeness  of  the  joint,  where  rivets  of  large  diameter  are 
used,  and  for  which  reasons,  in  preparing  the  table  given  in 
the  chapter  on  Riveting,  these  considerations  were  given 
weight.  In  the  mention  of  this  table,  it  may  not  be  out  of 
place  here  to  refer  to  the  dimensions  and  relative  strength  of 
the  double-butt  strap-joint,  and  to  point  out  that  while  fully 
recognizing  that  the  full  strength  of  such  a  joint  has  not  been 
developed,  the  necessity  for  such  excess  strength  over  and 
above  all  the  other  joints,  both  single,  double,  and  treble 
riveted,  did  not  seem  necessary  or  particularly  desirable. 

Machining:  Punching  and  Rolling. — After  the  plates  are 
laid  off  and  bevelled,  the  punching  of  rivet-holes  should  be 
done,  and  away  from  the  surfaces  to  be  in  contact.  Plates 
not  exceeding  f  inch  in  thickness  may  be  punched  with 
sharp  and  well-conditioned  punch  and  dies,  either  singly 
or  preferably  by  a  power-machine  employing  several  such 


278  TOWERS  AND    TANKS  FOR    WATER- WORKS. 

punches  or  dies,  properly  spaced.  The  area  of  the  rivet-hole 
should  be  about  Vie  incn  greater  than  that  of  the  rivet  pro- 
posed to  be  used. 

Plates  having  a  thickness  between  f  and  £  inches  should 
be  punched  1/16  inch  less,  and  reamed  out;  while  plates  over 
that  thickness  should  be  drilled  from  the  solid  sheet. 

While  it  has  been  shown  that  for  tank  work,  plates,  re- 
gardless of  thickness,  can  be  connected  in  a  more  mechanical 
fashion  by  requiring  the  horizontal  seams  to  be  a  lap  and 
the  vertical  joints  a  strap  connection,  for  reasons  of  econ- 
omy, the  lap-joint  is  used  and  will  probably  continue  tin  use 
for  connecting  all  plates,  for  both  horizontal  and  vertical 
seams,  where  the  thickness  of  the  plates  are  less  than  J  inch, 
and  possibly  a  thickness  of  13/i6  inch  should  be  considered 
as  the  maximum  permissible  thickness  for  the  use  of  a  lap- 
joint.  In  order  to  make  the  lap-connection,  a  corner  of  the 
plate  has  to  be  heated  and  drawn  out  to  make  the  joint  where 
three  plates  come  together.  This  drawing  out  after  heating 
is  called  "  scarfing,"  and  is  objectionable,  both  on  account  of 
the  unmechanical  joint  produced  and  as  well  as  from  the  fact 
that  this  reheating  and  working  of  the  steel  reduces  its 
strength,  as  has  been  explained  in  the  chapter  on  the  Phys- 
ical and  Chemical  Properties  of  Steel. 

When,  from  reasons  of  economy  or  other  necessity,  this 
reheating  is  permitted,  that  it  may  be  as  little  objectionable 
as  possible,  it  is  recommended  by  authorities  that  the  tem- 
perature of  the  metal,  and  which  permits  working,  shall 
range  between  a  heat  which  will  ignite  hard  wood  and  the 
boiling  temperature  of  water.  In  flanging  or  other  bending, 
it  is  sometimes  necessary  to  work  over  the  metal  in  this  way, 
but  for  bending  sheets  and  angles  to  radius  for  tank  work, 
heating  is  not  necessary  and  should  not  be  allowed,  it  being 
entirely  possible  to  bend  the  metal  to  the  required  shape 


• 


SHOP-PRACTICE  AND  ERECTION.  27 9 

when  cold  by  passing  it  through  powerful  steel  rolls;  this 
is  called  "  cold-rolling,"  and  should  always  be  specified. 

Such  rolling  should  invariably  follow  the  work  of  bevel- 
ling and  punching,  better  results  being  obtainable  through 
such  process. 

Shop-assembly. — Immediately  after  rolling,  the  various 
separate  parts  of  the  structure  should  be  assorted  and  "  as- 
sembled," to  insure  a  fair  and  satisfactory  arrangement  at  the 
point  of  erection.  Where  the  rivet-holes  do  not  match  per- 
fectly in  the  assembled  parts,  the  rivet-holes  should  be  made 
to  coincide  and  any  eccentricity  should  be  corrected  by 
reaming  out  the  hole  and  providing  for  a  larger  rivet. 

After  testing  the  several  members  during  this  "  shop- 
assembly,"  each  piece  should  be  regularly  and  carefully 
marked,  that  no  confusion  may  result  at  the  time  of  "  field  " 
or  final  assembly. 

Cleaning  and  Priming. — Immediately  after  testing  and 
correcting  the  shop-work,  the  parts  should  be  carefully 
cleaned  of  all  dirt,  grease,  mill-scale,  or  rust,  as  has  been 
explained,  preferably  by  the  use  of  the  sand-blast,  after 
which,  as  has  been  suggested,  a  coating  or  priming  should 
be  made  with  red  lead,  lampblack,  and  linseed-oil,  and  as 
soon  as  sufficiently  dry  for  handling,  the  material  should  be 
carefully  loaded  into  the  cars,  and  consigned  to  the  point  of 
erection. 

This  class  of  work  as  above  described  is  usually  done  by 
any  well-equipped  boiler-works,  and  the  shop-cost  is  about 
$20.00  per  ton,  exclusive  of  painting. 

During  the  progress  of  the  work,  independent  shop-in- 
spection should  be  insisted  upon  and  carried  out  by  an  ex- 
perienced and  reliable  inspector  whose  fee  would  amount  to 
approximately  40  to  50  cents  per  ton  of  material,  or  about 
$1.00  per  ton  for  complete  inspection  and  test  at  both  mill 
and  shop. 


280  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

Angles  and  other  shapes,  intended  to  form  such  a  super- 
structure as  a  tower,  are  usually  sheared,  milled,  and  con- 
nected by  riveting  at  a  well-equipped  bridge-works.  The 
same  precautions  as  to  riveting  and  cleaning  should  be  taken 
as  with  the  tank  work,  and  surfaces  in  contact  and  thereafter 
inaccessible  should  be  given  at  least  two  coats,  of  red  lead 
and  oil.  Only  connections  should  be  made  in  the  field,  all 
other  parts  being  riveted  in  the  shop  before  shipment. 

Preparation  of  Foundations. — To  avoid  what  is  known  as 
"  green  masonry,"  as  far  in  advance  as  possible  before  "  field- 
work,"  the  foundation  masonry  should  be  laid.  The  site  of 
the  structure  having  been  determined,  careful  tests  should 
be  made  to  determine  the  character  of  the  soil  and  to  ascer- 
tain its  bearing  value.  Such  tests  may  be  made  by  driving 
test-pits  with  such  an  implement  as  a  post-hole  digger,  or 
by  borings  made  with  an  auger  of  not  less  than  2-inch  diame- 
ter. The  auger-bit  is  welded  into  a  short  section  of  pipe; 
another  short  section  is  fitted  with  a  cross-piece  or  handle, 
and  additional  sections,  having  suitable  couplings,  are  to  be 
prepared  in  sufficient  number  to  permit  the  borings  to  be 
carried  to  a  safe  and  satisfactory  depth.  As  soon  as  expedi- 
ent after  such  borings,  and  the  design  of  a  foundation  to  sup- 
port the  structure,  excavations  are  made  and  the  sybfounda- 
tion  or  bearing  prepared.  The  character  of  the  connections 
for  the  anchorage  having  been  designed,  flat  planks  or 
boards  should  be  connected  in  such  a  way  as  to  form  a  suit- 
able templet,  which  should  be  carefully  laid  off  and  holes  of 
proper  size  bored.  The  anchor-rods  having  been  provided, 
these  are  usually  enclosed  in  old  boiler  or  other  tubes, 
slightly  larger  than  the  anchor-rods,  and  of  approximately 
the  same  length  or  a  little  shorter. 

The  rods  and  tubes  are  inserted  into  the  holes  of  the 
templet,  which  is  then  raised  to  the  correct  height  or  level 
and  made  fast  with  wooden  props  or  stays.  Each  of  the 


SHOP-PRACTICE  AND  ERECTION.  281 

washers  of  the  rods  are  then  carefully  levelled  and  the  rods 
plumbed,  generally  with  a  line  and  bob,  after  which  the 
masonry  is  commenced  and  continued  to  completion,  the 
tubes  remaining  in  place  until  that  time,  when  they  are  with- 
drawn, leaving  a  space  about  the  anchor-rod,  which  allows 
slight  adjustment  of  the  rod  to  suit  the  connection  when 
placed. 

Upon  the  completion  of  the  masonry,  the  templet  and 
braces  are  removed,  the  rods  tested  and  adjusted,  and  the 
spaces  about  them  filled  with  cement  grout,  as  thick  as  can 
be  poured. 

All  series  of  levels  taken  should  be  carefully  recorded,  and 
should  refer  to  a  permanent  "  bench-mark  "  or  datum.  In 
this  way,  any  irregularity  during  construction  may  be  cor- 
rected and  any  subsequent  settlement  may  be  noted. 

In  the  foundations  for  the  usual  tower,  the  templet  for  the 
rods  and  tubes  is  generally  formed  of  a  single  plank,  thick 
enough  to  prevent  sagging,  and  which  is  accurately  placed 
across  the  foundation-pit,  buried  flush  with  the  earth,  and 
frequently  fastened  or  staked  down  to  prevent  disturbance. 
The  rods  are  passed  through  suitable  holes  bored  in  this 
plank,  levelled  and  plumbed.  It  is  hardly  necessary  to  re- 
mark that  each  of  these  foundation-pits  require  a  separate 
plank. 

Preliminaries  to  Erection  of  Stand-pipes. — The  founda- 
tions being  ready  to  receive  the  superstructure,  provision 
should  be  made  for  carefully  unloading  the  material  upon  its 
arrival,  for  which  purpose,  ordinarily,  a  short  "  gin-pole," 
with  a  metal  hook  or  rope  sling  at  its  top,  and  guyed  in  a 
vertical  position  and  adjacent  to  the  transfer  track  is  found 
convenient. 

Great  care  should  be  taken  to  prevent  bending  any  of 
the  sections  or  rubbing  or  scratching  the  surface  which 
should  have  been  primed. 


282  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

Arrived  at  the  foundations,  the  sheets  should  be  sys- 
tematically placed,  the  bottom  pieces  and  angles  being  near- 
est; the  top  pieces,  cresting,  etc.,  furthest  away  from  the 
foundations. 

Upon  the  top  or  face  of  the  foundation,  it  is  customary  to 
place  the  kegs  of  rivets,  which  being  of  the  same  height, 
make  a  sort  of  platform  upon  which  the  bottom  plates  may 
be  put  together. 

After  these  have  been  riveted  to  each  other  and  to  the  cir- 
cumscribing angles  which  fasten  the  bottom  and  shell,  the 
tightness  of  the  bottom  is  tested  by  pouring  water  upon  the 
plates.  If  the  joints  are  not  found  to  be  tight,  they  are  fur- 
ther calked,  or  if  the  leak  is  due  to  imperfect  or  loose  rivet- 
ing, such  rivets  are  cut  away  with  chisel  and  sledge;  the  hole 
is  reamed  larger  and  a  larger  rivet  inserted  and  driven. 

Field- assembly. — These  preliminaries  having  been  ob- 
served, about  the  outer  circumference  of  the  foundations  a 
slight,  low  dam  of  clay  puddle  or  even  of  sand  is  constructed; 
into  the  area  so  formed  is  then  slushed  or  poured  a  rich 
cement  grout,  sufficient  to  cover  the  face  of  the  foundations 
and  deep  enough  to  entirely  cover  and  hide  the  heads  of  the 
rivets  upon  the  under  side  of  the  bottom  plates.  Having 
been  quickly  "  floated  "  or  levelled  over,  the  bottom  of  the 
tank  is  lowered  as  rapidly  as  possible,  by  means  of  jacks  or 
levers. 

The  separate  sheets  of  the  first  ring  are  then  set  in  posi- 
tion, being  temporarily  bolted  to  place  and  afterwards 
riveted. 

As  each  sheet  is  placed,  the  surfaces  in  contact,  or  the 
joint  surfaces,  should  be  given  another  coat  of  thick  red  lead 
and  oil,  as  should  also  the  joint  after  riveting,  that  the  rivet- 
heads  may  be  entirely  covered  to  prevent  the  formation  of 
rust  during  construction  and  before  the  finishing  coats  of 
paint  are  supplied. 


t 
SHOP-PRACTICE  AND  ERECTION.  283 

With  the  second  and  succeeding  rings,  a  short  "  gin- 
pole  "  -is  first  bolted  to  the  top  rivet-holes  of  the  section 
below,  and  sheets  are  hoisted  in  succession  and  temporarily 
fastened  with  bolts  until  the  entire  circle  has  been  so  placed, 
when  riveting  is  begun,  the  heating-forge  being  conveniently 
located  in  a  travelling-carriage  or  "  cage,"  moving  along  the 
circumference  upon  small  rollers  or  trolleys  as  required, 
while  the  riveter,  forming  the  field-heads  with  a  forming- 
hammer,  upon  the  head  of  which  two  men  strike  with 
sledges,  remains  upon  the  inside  of  the  structure,  all  the 
workmen  standing  upon  scaffolding,  which  is  raised  as  the 
work  proceeds,  and  which  may  consist  of  2"  X  2"  uprights. 

Upon  the  completion  of  the  metal-work  of  the  shell,  the 
ornamental  cresting  or  cover,  the  ladders  and  other  fittings 
and  trimmings  are  put  in  position;  the  tank  then  being  ready 
for  testing,  is  filled  with  water.  Leaks  along  the  seams  are 
caulked  carefully,  but  no  caulking  should  be  permitted  upon 
leaks  about  rivet-heads,  due  to  imperfectly-filled  rivet-holes 
or  loose  rivets.  Such  rivets  should  be  cut  out  with  chisel 
and  sledge;  the  hole  reamed  out  and  larger  rivets  driven. 
Such  leaks  are  carefully  marked  while  the  water  is  in  the 
tank  and  the  repairs  made  after  the  vessel  is  emptied.  No 
caulking  or  chipping  should  be  allowed  while  the  water  re- 
mains in  the  tank.  The  hoisting  of  plates  is  usually  done  by 
hand,  using  a  winch,  from  which  a  line  passes  through  a  block 
hung  from  a  loop  or  hook  on  the  "  gin-pole,"  and  to  which 
is  attached  some  form  of  tongs  or  "  grab,"  which  may  be 
hooked  into  the  rivet-holes  of  the  sheet  to  be  hoisted.  A 
"  riveting  crew,"  or  gang,  consists  usually  of  a  foreman, 
who  also  personally  does  the  caulking  of  seams;  a  riveter, 
generally  an  experienced  boiler-maker;  a  skilful  "  heater," 
who  heats  the  rivets  to  a  forging  heat  and  passes  them  in 
tongs  into  the  rivet-holes,  and  three  laborers,  one  of  whom 
directs  a  heavy  suspended  weight  against  the  rivet  being 


284  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

driven,  while  the  other  two  strike  in  turn  upon  the  hammer 
held  by  the  riveter  in  forming  the  field-head.  Two  extra 
laborers  are  generally  employed  to  work  at  the  winch  and  to 
sort  out  material  as  directed  by  the  foreman. 

Such  a  crew  will  drive  from  400  to  500  rivets  per  day  of 
ten  hours,  at  a  cost  of  3  cents  each,  or  the  entire  cost  of 
erection,  including  riveting,  will  amount  to  about  $20.00  per 
ton  of  material.  The  scaffolding  is  left  in  place  upon  the  in- 
side of  the  tank  until  after  testing  by  filling.  The  tank  being 
tight,  it  is  then  removed.  Instead  of  the  scaffold  as  de- 
scribed, a  floating  scaffold  is  sometimes  employed,  which 
consists  of  a  buoyant  platform  or  float  that  is  raised  to 
position  as  required  by  pumping  water  into  the  tank. 

Inspection. — After  inspection  and  approval  of  the  metal- 
work  and  the  emptying  of  the  water  used  in  testing,  the  in- 
terior surfaces  should  be  wiped  dry  with  oily  cloths,  and  the 
final  coating  or  painting  given,  the  scaffolding  being  re- 
moved as  the  painting  proceeds  from  the  top  downward.  In 
view  of  the  fact  that  a  heavy  gale  is  liable  to  seriously  affect 
the  joints  of  the  stand-pipe  if  empty,  by  straining  the  struc- 
ture, immediately  upon  the  drying  of  the  paint,  the  reservoir 
should  be  filled  with  water  and  kept  so  filled  until  put  into 
actual  use  as  part  of  the  water  system. 

Erection  of  Towers  and  Tanks. — In  the  erection  of  a 
tower,  the  pedestal-plates  should  be  bedded  in  cement  mor- 
tar about  an  inch  thick.  The  first  step  toward  erection  is  to 
conveniently  place  the  columns  and  members  of  the  first  panel 
or  section,  and  in  such  position  that,  with  the  aid  of  a  stout 
gin-pole,  blocks,  tackle,  and  winch,  the  columns  may  be 
simultaneously  raised  to  their  vertical  position  and  the  hori- 
zontal members  placed  and  temporarily  fastened  with  bolts, 
to  be  subsequently  riveted  before  proceeding  with  the  next 
panel  or  deck. 

As  has  been  remarked,  the  field-riveting  should  be  con- 


SHOP-PRACTICE  AND  ERECTION.  285 

fined  entirely  to  panel-points  or  points  of  connection,  all 
other  rivet-work  having  previously  been  done  at  the  shop. 

The  first  panel  having  been  secured,  a  smaller  gin-pole 
is  bolted  to  each  of  the  columns  or  legs  in  succession,  and  the 
next  vertical  member  is  raised  to  its  place  and  fastened  by 
bolts  until  all  of  the  column-sections  are  so  located,  when  the 
horizontal  and  diagonal  members  are  hoisted  into  position 
and  secured.  When  the  last  or  upper  panel  is  in  place,  where 
the  structure  is  surmounted  with  a  platform,  this  is  erected, 
from  which  work  conveniently  proceeds  upon  the  girders, 
bottom,  and  subsequent  tank-sections  or  rings,  as  has  been 
described. 

An  approximate  cost  of  such  work  is  $25.00  per  ton  of 
material,  varying  with  the  local  conditions  at  the  point  of 
erection. 

Field-riveting  and  Machine-driven  Rivets. — As  the  field- 
work  consists  largely  of  riveting  the  members  together, 
the  following,  taken  from  the  Locomotive,  a  paper  pub- 
lished by  the  Hartford  Steam-boiler  Inspection  and  Insur- 
ance Company,  may  be  of  interest:  "  The  driving  of  rivets 
is  such  a  comparatively  simple  operation,  that  it  might  be 
supposed  that  it  would  be  almost  always  well  done.  This  is 
far  from  being  the  fact,  however,  and  bad  riveting  is  one  of 
the  commonest  defects  reported  by  our  inspectors. 

'  The  rivets  may  be  too  short,  or  too  long,  or  too  small; 
they  may  have  heads  that  are  too  flat,  or  they  may  have  pro- 
jecting '  fins,'  or  they  may  not  fill  the  holes,  or  the  holes  may 
not  come  '  fair  '  with  one  another.  There  are  many  ways 
in  which  riveting  may  be  bad.  .  .  ."  In  reporting  a  particu- 
lar case  of  imperfect  rivet-work  in  the  same  article,  is  the  fol- 
lowing: "  The  inspector  found  the  rivets  '  driven  very  low '' 
— that  is,  the  heads  were  entirely  too  flat.  He  had  a  num- 
ber of  these  rivets  taken  out,  and  found  that  the  holes  in  the 
two  sheets  did  not  come  opposite  one  another  fairly.  This 


286  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

defect  is  a  common  one,  and  it  is  very  serious,  both  because 
it  reduces  the  shearing-area  of  the  rivet,  and  because  it 
greatly  increases  the  difficulty  of  making  the  rivets  fill  the 
holes  perfectly.  A  shop  that  turns  out  work  of  this  kind  is 
particularly  censurable,  not  only  because  the  work  itself  is 
poor  and  weak,  but  also  because  the  defect  is  not  easy  to  dis- 
cover, after  the  rivets  are  in  place,  and  the  owner  of  the  boiler 
is  therefore  likely  to  be  deceived  by  a  fair  external  appear- 
ance, and  to  carry  more  pressure  than  the  boiler  can  safely 
withstand.  The  inspector  also  found  that  the  heads  were 
not  driven  evenly  over  the  holes,  the  centres  of  the  heads 
often  lying  well  towards  the  side  of  the  rivet.  This  defect, 
although  not  so  dangerous  as  the  unfairness  of  the  holes, 
would  not  be  tolerated  in  a  good  shop  having  any  pretense 
of  turning  out  first-class  work.  It  is  very  easily  detected, 
even  by  one  who  has  had  little  experience  in  inspecting; 
and  there  is  no  excuse  for  it  whatever.  .  .  .  The  only  thing 
that  could  be  done  in  the  way  of  improvement  would  be  to 
cut  out  all  the  rivets,  ream  out  the  holes  until  they  should  be 
true,  and  rivet  them  up  again  with  larger  rivets." 

There  are  many  reasons  for  the  belief  that  a  machine- 
driven  rivet  makes  a  much  more  satisfactory  job  than 
where  a  rivet  is  driven  by  hand,  for  the  metal  cooling  rapidly, 
the  greatest  power  and  certainty  is  required  to  forge  the  head 
before  the  rivet  material  is  too  cold  to  work.  Various  types 
of  power  riveting-machines  are  now  built  whose  motor  force 
is  either  air,  steam,  water  or  electricity,  affording  a  constant 
pressure  throughout  the  stroke  of  about  80  pounds. 

From  comparative  tests  with  both  power-  and  hand- 
driven  rivets,  in  Kent's  "  Mechanical  Engineer's  Handbook," 
is  recorded  the  slip  of  plates  pulled  apart.  In  this  it  is  shown 
that  machine-driven  rivets  of  equal  diameter  held  twice  as 
much  as  hand-driven  rivets. 

At  the  Gas  Exhibition,  held  in  New  York  about  1897, 


. 


SHOP-PRACTICE  AND  ERECTION.  28/ 

samples  of  heavy  plates  riveted  by  both  hand-  and  machine- 
work  were  split  with  a  saw,  and  the  rivets  and  holes  shown 
in  cross-section.  All  machine-driven  rivets  completely  rilled 
the  rivet-holes,  while  the  hand-work  was  seen  to  be  very 
irregular.  In  his  work  entitled  "  Iron  Highway  Bridges," 
and  in  connection  with  suggestions  for  riveting,  the  follow- 
ing is  given  by  Mr.  Alfred  P.  Boiler,  M.  Am.  Soc.  C.  E. : 
"  Power-riveting  is  so  superior  in  all  respects  to  hand-rivet- 
ing that  a  higher  unit  of  strain,  by  probably  10  per  cent.,  can 
be  used  under  the  former  system;  so  that  if  it  is  considered 
proper  to  strain  hand-rivet  work  up  to  13,500  Ibs.  per  square 
inch,  work  riveted  up  by  steam  or  hydraulic  power  can  be 
safely  proportioned  on  a  basis  of  15,000  Ibs.  per  square  inch." 

So  clearly  is  the  superiority  of  power-riveting,  that  it  is 
specified  almost  exclusively  for  boiler-work,  bridge-work,  and 
in  fact  for  almost  all  shop-work,  but  its  use  in  the  field  is  com- 
paratively limited  and  of  recent  date.  In  this  connection,  the 
Engineering  Neivs  for  May,  1895,  publishes  a  description  of 
a  stand-pipe  erected  at  St.  Barnard,  by  L.  Schreiber  &  Sons 
Co.,  of  Cincinnati,  Ohio,  who  used  for  the  field-work  a  pneu- 
matic riveting-machine,  suspended  from  a  -hoist  by  the 
arm  of  a  crane  with  mast  in  the  centre  of  the  shell.  In  re- 
sponse to  an  inquiry  as  to  this  work  and  as  to  the  cost  and 
efficiency  of  power  field-riveting  in  general,  Messrs.  Schrei- 
ber &  Sons  Co.  reply  "  that  we  have  found  pneumatic  rivet- 
ing much  better  than  hand-work,  especially  so  if  the  machin- 
ery is  of  the  proper  kind.  We  do  this  work  under  very  high 
pressure  and  hardly  believe  (owing  to  the  fact  that  the  ma- 
chinery required  for  this  work  is  very  heavy)  that  there  is  a 
great  saving  over  hand-riveting.  However,  there  is  a  little 
in  favor  of  the  machine-riveting." 

The  Logan  Iron  Works,  contractors  for  a  stand-pipe  at 
College  Point,  L.  L,  used  a  pneumatic  riveting-machine  in 
driving  some  75,000  rivets.  According  to  information  re- 


288  TOWERS  AND    TANKS  FOR    WATER-WORKS, 

ceived  from  the  manufacturer  of  this  machine,  "  not  a  single 
rivet  had  to  be  cut  out  or  caulked,  a  most  exceptional  record 
which  has  not  been  equalled  by  any  other  machine.  They 
drove  800  to  1200  rivets  per  day,  depending  on  size.  They 
tell  me  the  cost  of  driving  by  machine  was  less  than  half  that 
of  driving  by  hand.  Allowing  three  men  and  a  boy  on  ma- 
chine, at  $9.00  per  day  and  $4.50  for  cost  of  running  air- 
compressor  and  fuel,  or  $13.50  per  day  for  crew,  this  makes 
a  cost  of  about  one  to  one  and  a  half  cents  per  rivet." 

A  quotation  from  a  communication  to  the  Engineering 
News  from  Mr.  Freeman  C.  Coffin,  M.  Am.  Soc.  C.  E.,  will 
be  used  in  concluding  this  subject,  and  is  as  follows:  "  The 
rivets  should  be  driven  by  steam  or  hydraulic  power.  This 
may  seem  radical,  but  I  do  not  think  so.  I  see  no  real  rea- 
son why  it  could  not  be  done  with  the  suitable  appliances. 
If  field-riveting  can  be  done  by  power  in  any  structure,  a 
stand-pipe  is  the  best  form,  as  there  are  continuous  rows  of 
rivets  of  about  the  same  diameter,  and  the  only  especial  form 
of  appliance  would  be  the  yoke  of  the  riveter,  which  would 
need  to  straddle  a  5-foot  plate.  I  do  not  believe  that  this  is 
impracticable.  I  think  it  must  hurt  the  feelings  of  any  engi- 
neer to  see  two  men  with  heavy  sledges  pounding  away  at 
a  cool  rivet,  endeavoring  to  form  a  head  on  it.  The  usual 
result  is  a  very  thin,  flat  head,  as  the  rivets  are  used  as  short 
as  possible  in  order  not  to  cause  too  much  trouble  if  they 
happen  to  get  cold  before  they  are  finished." 


CHAPTER  XIII. 

SPECI  FICATIONS. 

NECESSARILY  the  briefest  allusion  to  and  the  faintest  outline 
of  the  fundamental  principles  of  engineering  jurisprudence,  or 
the  law  of  contracts  for  constructive  work  is  possible  or  allowable 
here. 

Usually  the  construction  of  metallic  reservoirs  are  incident 
to  the  building  of  entire  systems  of  water- works  for  municipal 
supply,  and  the  general  agreement  governing  such  construction 
and  incorporated  into  the  forms  of  a  contract  apply  equally  to 
this  particular  item  of  the  whole  work. 

Suitable  forms  of  agreement  are  dictated  by  the  necessities 
and  the  general  understanding  of  the  particular  case,  covering 
in  a  general  way  the  character  of  the  work  to  be  performed, 
whose  details  are  more  fully  set  forth  and  particularly  described 
through  the  wording  of  the  "specifications."  As  the  draft  of 
such  an  instrument  as  a  legal  contract  for  important  work,  such  as 
the  construction  of  a  water  system,  falls  frequently  to  the  lot 
of  the  professional  legal  adviser,  requiring  of  the  engineer  simply 
the  technical  description  or  the  specifications  intended  to  govern 
the  constructive  work,  no  analysis  will  be  attempted  of  the  forms 
of  contract  and  recognized  procedure  in  such  cases;  but  since 
it  is  the  province  and  duty  of  the  engineer  to  prepare  plans  and 
to  describe  in  detail  the  technical  features  of  the  work,  and  as 
the  incorporation  of  the  principles  and  practices  heretofore 
enunciated  in  the  preceding  pages  is  undoubtedly  pertinent 
and  proper,  a  general  form  and  brief  discussion  of  the  specific 

289 


290  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

requirements  intended  to  govern  the  construction  of  a  structural 
steel  tower  and  tank  are  hereinafter  included.  Inasmuch  as 
metal,  design,  and  workmanship  prescribed  are  applicable  gen- 
erally as  well  to  such  structures  as  stand-pipes,  separate  specifi- 
cations for  the  latter  type  will  be  omitted. 

Municipalities,  corporations,  or  individuals,  called  upon  to 
perform  constructive  work  of  magnitude  and  importance,  seldom 
undertake  its  execution,  necessarily  relying  upon  skilled  mechanics 
and  artisans  employed  and  controlled  by  individuals  of  practical 
and  financial  ability,  who,  for  adequate  consideration,  undertake 
to  perform  the  work  required  within  a  stated  time.  This  under- 
taking is  generally  expressed  in  a  written  instrument  of  agree- 
ment known  as  a  contract  and  the  work  is  performed  under 
the  penalty  expressed  in  a  bond. 

An  essential  element  of  a  valid  contract  is  that  there  be  a  per- 
fect and  well-defined  understanding  and  mutual  consent  between 
the  parties.  The  usual  manner  of  reaching  a  mutual  under- 
standing, especially  when  the  character  of  the  work  contemplated 
is  of  considerable  magnitude,  and  its  execution  requires  technical 
training  and  experience,  is  by  invitation,  public  or  private  solici- 
tation, as  by  advertisement  for  proposals,  which  negotiations, 
conducted  by  municipalities  or  individuals,  carry  with  them 
the  right  of  creating  completing,  and  determining  a  contract 
through  the  unreserved  acceptance  of  one  of  the  proposals  solicited 
when  made  in  absolute  and  unconditional  terms. 

Often  the  requirement  of  a  statute  makes  the  form  of  invitation 
or  advertisement  mandatory;  describes  what  degree  of  publicity 
shall  be  necessary,  and  in  such  cases  any  violation  of  the  legal 
terms  are  fatal  to  the  validity  of  the  contract. 

In  order  that  free  and  fair  competition  be  secured  and  that 
favoritism,  collusion,  combination,  and  fraud  be  minimized,, 
statutory  acts  generally  prescribe  due  notice  by  advertisement 
of  the  intent  pf  the  municipality  to  enter  into  a  contract  for  a 
specific  purpose;  frequently  the  form  of  advertisement  is  ex- 


SPECIFICA  TIONS.  29 1 

plicitly  indited,  stipulating  such  general  information  as  may  be 
deemed  sufficient  for  the  notice  and  guidance  of  prospective 
bidders  and  stating  the  formalities  incident  to  the  proposal. 

To  obtain  reasonable,  fair,  and  intelligent  competition  is 
the  legitimate  object  of  all  such  advertisements  for  proposals, 
to  secure  which  it  is  imperative  that  the  relative  value  of  all 
offers  be  submitted  to  scrutiny  and  comparison  upon  precisely 
the  same  terms;  hence  it  becomes  the  duty  of  those  authorized 
to  conduct  such  negotiations  to  cause  to  be  prepared,  either 
graphically,  by  descriptive  phraseology,  or  both,  what  is  technically 
and  respectively  known  as  "the  plans"  and  " specifications " 
to  be  used  primarily  for  the  information  of  bidders,  and  event- 
ually to  be  incorporated  into  the  body  of  the  contract  expressing 
the  mutual  obligations  of  the  contracting  parties. 

In  drafting  a  contract  it  is  necessary  to  the  integrity  of  the 
instrument  that  the  exact  understanding  of  the  parties  to  the 
agreement  should  be  stated  in  precise  terms;  ample  provision 
must  be  made  not  only  for  present  conditions,  but  to  cover  future 
emergencies  or  contingencies,  while  the  technicalities  of  the  law 
must  be  strictly  followed  and  adhered  to  throughout.  Hence,  as 
has  been  said,  in  important  contracts  it  is  usual  to  entrust  the  prep- 
aration of  such  instruments  to  legal  advisers,  while  necessarily,  in- 
constructive  contracts,  engineering  details  are  left  to  the  engineer- 
ing expert,  the  collaboration  frequently  resulting  in  errors,  mis- 
understandings, and  discrepancies  between  the  terms  of  the 
contract  and  the  intent  of  the  specifications. 

In  cases  of  resulting  differences,  the  intent  of  the  parties 
will  be  sought  and  established  if  possible,  but  in  the  absence  of 
conclusive  evidence  as  to  what  was  meant,  the  contract  itself  is 
of  the  first  importance,  as  it  represents  the  instrument  by  which 
the  obligation  to  perform  the  work  or  to  furnish  the  material  is 
assumed,  and  there  is  a  tendency  to  give  greater  weight  to  it  than 
to  the  plans  and  specifications  which  are  chiefly  descriptive  of 
the  work  and  the  manner  of  its  performance  and  which  are  almost 


292  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

always  subject  to  change  or  modification.  It  is  possible  that 
the  secondary  place  given  the  specifications  where  litigation  has 
arisen  may  be  due  to  the  fact  that  the  court  necessarily  is  more 
familiar  with  the  law  of  contracts  than  with  the  mechanics  of 
engineering.  However,  a  little  care  in  drafting  a  contract,  includ- 
ing specifications,  will  prevent  inaccuracy  or  ambiguity. 

While  the  exact  intent  of  the  parties  should  be  understood 
and  carefully  and  accurately  incorporated  into  the  body  of  the 
contract  through  its  phraseology,  the  terms  of  the  specifications, 
while  intended  as  a  collateral  and  integral  part  of  this  instrument, 
should  be  exact  in  meaning  and  expression,  but  not  necessarily 
minute  as  to  detail,  as  unnecessary  refinement  is  more  likely 
to  lead  to  confusion  and  misunderstanding  than  to  clear  com- 
prehension. 

Whilst  generalities  should  be  scrupulously  avoided,  specifica- 
tions should  be  so  drawn  that  a  broad  treatment  and  interpreta- 
tion of  the  particular  matter  should  be  possible,  as  results,  re- 
gardless of  specific  limitations  and  narrow  exactions,  should 
l>e  attempted,  and  in  almost  any  specific  case  a  greater  success 
will  undoubtedly  be  secured  by  permitting  individuality  and  a 
certain  latitude  in  the  design  and  execution  of  the  particular 
work. 

This  freedom  for  individual  expression  should  not  be  so 
licensed  as  to  prove  embarrassing  in  allowing  competition  along 
lines  where  comparison  is  impossible  and  relative  merit  inde- 
terminate, nor  yet  such  as  would  offer  a  premium  or  lead  com- 
petitors, in  the  keenness  of  commercial  rivalry,  into  experimental 
practice  to  an  extent  where  failure  would  prove  disastrous  unless 
the  responsibility  for  such  failure  has  been  discounted  in  advance 
and  the  liability  for  a  possible  disaster  has  been  clearly  placed 
where  it  properly  belongs — upon  the  promoter  or  experimenter. 
In  the  preparation  of  the  specifications  for  structural  work  no 
deviation  from  a  high  and  comprehensive  standard  as  to  the 
quality  of  the  materials  and  workmanship  should  be  permitted, 


SPECIF2CA  TIONS.  293 

encouraged,  or  made  possible;  but,  as  has  been  said,  the  general 
instructions  should  be  such  as  would  encourage  individuality 
of  design  and  construction,  where  such  latitude  is  likely  to  elevate 
and  cannot  possibly  lower  the  scale  of  general  excellence  sought. 

What  has  been  said  presents  rather  the  legal  than  the  com- 
mercial aspect  of  a  draft  of  a  set  of  specifications,  but  beside  the 
legality  of  the  transaction,  vital  though  this  be,  the  technical 
and  trade  elements  are  primarily  the  most  essential.  The  rule 
that  "the  best  is  the  cheapest  in  the  end"  has  its  limitations. 
For  a  building,  to  specify  all  "hard"  brick  and  "heart  lumber" 
entails  upon  the  purchaser  an  unnecessary  expense  where,  in 
general,  "kiln- run"  brick  and  "merchantable"  lumber  would 
answer  every  practical  requirement;  nor  should  the  engineer 
expect  to  get  high-grade  materials  for  his  client  by  ambiguity 
and  his  interpretation  of  the  specifications. 

Before  commencing  to  draft  specifications,  what  is  wanted 
must  be  fully  known,  expressed  without  ambiguity  and  useless 
verbiage,  and  afterwards  insisted  upon. 

In  a  recent  address,  delivered  before  the  American  Society 
for  Testing  Materials,  Dr.  Chas.  B.  Dudley,  Chief  Chemist 
of  the  Pennsylvania  Railroad  Company,  crystallizes  these  princi- 
ples in  his  conclusions,  which  are  as  follows: 

"  (i)  A  specification  for  material  should  contain  the  fewest 
possible  restrictions  consistent  with  obtaining  the  material 
desired. 

"  (2)  The  service  which  the  material  is  to  perform,  in  con- 
nection with  reasonably  feasible  possibilities  in  its  manufacture, 
should  determine  the  limitations  of  a  specification. 

"  (3)  All  parties  whose  interests  are  affected  by  a  specification 
should  have  a  voice  in  its  preparation. 

"  (4)  The  one  who  finally  puts  the  wording  of  the  specification 
into  shape  should  avoid  making  it  a  place  to  show  how  much 
he  knows,  as  well  as  a  mental  attitude  of  favor  or  antagonism 
to  any  of  the  parties  affected  by  it. 


294  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

"  (5)  Excessively  severe  limitations  in  a  specification  are  suici- 
dal. They  lead  to  constant  demands  for  concessions,  which  must 
be  made  if  work  is  to  be  kept  going,  or  to  more  or  less  successful 
efforts  at  evasion.  Better  a  few  moderate  requirements  rigidly 
enforced  than  a  mass  of  excessive  limitations,  which  are  difficult 
of  enforcement,  and  which  lead  to  constant  friction  and  sometimes 
to  deception. 

"  (6)  There  is  no  real  reason  why  a  specification  should  not 
contain  limitations  derived  from  any  source  of  knowledge.  If 
the  limitations  shown  by  physical  test  are  sufficient  to  define 
the  necessary  qualities  of  the  material,  and  this  test  is  simplest 
and  easiest  made,  the  specification  may  reasonably  be  confined 
to  this.  If  a  chemical  analysis  or  a  microscopic  examination, 
or  a  statement  of  the  method  of  manufacture,  or  information 
from  all  four,  or  even  other  sources,  are  found  useful  or  valuable 
in  defining  limitations,  or  in  deciding  upon  the  quality  of  material, 
there  is  no  legitimate  reason  why  such  information  should  not 
appear  in  the  specifications.  Neither  the  producer  nor  the 
consumer  has  a  right  to  arrogate  to  himself  the  exclusive  right 
to  use  information  from  any  source. 

"  (7)  Proprietary  articles  and  commercial  products  made  by 
processes  under  the  control  of  the  manufacturer  cannot,  from 
the  nature  of  the  case,  be  made  the  subject  of  specifications. 
The  very  idea  of  a  specification  involves  the  existence  of  a  mass 
of  common  knowledge  in  regard  to  any  material,  which  knowledge 
is  more  or  less  available  to  both  producer  and  consumer.  If  the 
manufacturer  or  producer  has  opportunities,  which  are  not 
available  to  the  consumer,  of  knowing  how  the  variation  of  certain 
constituents  in  his  product  will  affect  that  product  during  manu- 
facture, so  also  does  the  consumer,  if  he  is  philosophic  and  is  a 
student,  have  opportunities,  not  available  to  the  producer,  of  know- 
ing how  the  same  variation  of  constituents  in  the  product  will 
affect  that  product  in  service,  and  it  is  only  by  the  two  working 


SPECIFICA  TIONS.  2$$ 

together,  and  combining  the  special  knowledge  which  each  has, 
that  a  really  valuable  specification  can  be  made. 

"  (8)  A  complete  workable  specification  should  contain  the 
information  needed  by  all  those  who  must  necessarily  use  it,  in 
obtaining  the  material  desired.  On  railroads  this  may  involve 
the  purchasing  agent,  the  manufacturer,  the  inspector,  the  engineer 
of  tests,  the  chemist,  and  those  who  use  the  material.  A  general 
specification  may  be  limited  to  describing  the  properties  of  the 
material,  the  method  of  sampling,  the  amount  covered  by  one 
sample,  and  such  descriptions  of  the  tests  as  will  prevent  doubt 
or  ambiguity. 

"  (9)  Where  methods  of  testing  or  analysis  or  inspection  are 
well  known  and  understood  it  is  sufficient  if  the  specification 
simply  refers  to  them.  Where  new  or  unusual  tests  are  required, 
or  where  different  well-known  methods  give  different  results, 
it  is  essential  to  embody  in  the  specification  sufficient  description 
to  prevent  doubt  or  ambiguity. 

"  (10)  The  sample  for  test  representing  a  shipment  of  material 
should  always  be  taken  at  random  by  a  representative  of  the 
consumer. 

"  (n)  The  amount  of  material  represented  by  one  sample  can 
best  be  decided  by  the  nature  of  the  material,  its  importance, 
and  its  probable  uniformity,  as  affected  by  its  method  of  manu- 
facture. No  universal  rule  can  be  given. 

"  (12)  The  purchaser  has  a  right  to  assume  that  every  bit  of 
the  material  making  up  a  shipment  meets  the  requirements  of 
the  specification,  since  that  is  what  he  contracted  for  and  expects 
to  pay  for.  It  should  make  very  little  difference,  therefore,  what 
part  of  the  shipment  the  sample  comes  from  or  how  it  is  taken. 
Average  samples,  made  up  of  a  number  of  sub-samples,  are  only 
excusable  when  the  limits  of  the  specification  are  so  narrow  that 
they  do  not  cover  the  ordinary  irregularities  of  good  practice 
in  manufacture. 

"  (13)  Retests  of  material  that  has  once  failed  should  only 


296  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

be  asked  for  under  extraordinary  conditions,  and  should  be  granted 
even  more  rarely  than  they  are  asked  for,  errors  in  the  tests  of 
course  excepted. 

11  (14)  Simple  fairness  requires  that  when  it  is  desired  that 
material  once  fairly  rejected  should  nevertheless  be  used,  some 
concession  in  price  should  be  made. 

"  (I5)  Where  commercial  transactions  are  between  honorable 
people,  there  is  no  real  necessity  for  marking  rejected  material 
to  prevent  its  being  offered  a  second  time.  If  it  has  failed  once, 
it  will  probably  fail  a  second  time,  and  if  return  freight  is  rigidly 
collected  on  returned  shipments  the  risk  of  loss  is  greater  than, 
most  shippers  will  care  to  incur.  Moreover,  it  is  so  easy  for  the 
consumer  to  put  an  inconspicuous  private  mark  on  rejected 
material,  that  it  is  believed  few  will  care  to  incur  the  probable 
loss  of  business  that  will  result  from  the  detection  of  an  effort 
to  dispose  of  a  rejected  shipment  by  offering  it  a  second 
time. 

"  (16)  All  specifications  in  actual  practical  daily  use  need 
revision  from  time  to  time,  as  new  information  is  obtained,  due 
to  progress  in  knowledge,  changes  in  methods  of  manufacture, 
and  changes  in  the  use  of  materials.  A  new  specification — that 
is,  one  for  a  material  which  has  hitherto  been  bought  on  the  reputa- 
tion of  the  makers  and  without  any  examination  as  to  quality — 
will  be  fortunate  if  it  does  not  require  revision  in  from  six  to  ten 
months  after  it  is  first  issued. 

"  (17)  In  the  enforcement  of  specifications,  it  is  undoubtedly  a. 
breach  of  contract  legitimately  leading  to  a  rejection  if  the  specified 
tests  give  results  not  wholly  within  the  limits,  and  this  is  especially 
true  if  the  limits  are  reasonably  wide.  But  it  must  be  remembered 
that  no  tests  give  the  absolute  truth,  and  where  the  results  are 
near,  but  just  outside  of  the  limit,  the  material  may  actually 
be  all  right.  It  seems  to  us  better,  therefore,  to  allow  a  small 
margin  from  the  actual  published  limit,  equal  to  the  probable 
limit  of  error  in  the  method  of  testing  employed,  and  allow  for 


SPECJF2CA  TIONS. 

this    margin   in  the  original  limits  when  the  specifications  are 
drawn. 

"  (18)  Many  producers  object  to  specifications  on  the  ground 
that  they  are  annoying  and  harassing,  and  really  serve  no  good 
purpose.  It  is  to  be  feared  that  the  complaint  is  just  in  the 
cases  of  many  unwisely  drawn  specifications.  But  it  should 
be  remembered  that  a  good  reasonable  specification,  carefully 
worked  out,  as  the  result  of  the  combined  effort  of  both  producer 
and  consumer,  and  which  is  rigidly  enforced,  is  the  best  possible 
protection  which  the  honest  manufacturer  can  have  against 
unfair  competition. 

"  (19)  Many  consumers  fear  the  effect  of  specifications  on 
prices.  Experience  seems  to  indicate  that  after  a  specification 
has  passed  what  may  be  called  the  experimental  stage,  and  is 
working  smoothly,  prices  show  a  strong  tendency  to  drop  below 
figures  prevailing  before  the  specification  was  issued. 

"  (20)  A  complete  workable  specification  for  material  represents 
a  very  high  order  of  work.  It  should  combine  within  itself  the 
harmonized  antagonistic  interests  of  both  the  producer  and  the 
consumer,  it  should  have  the  fewest  possible  requirements  con- 
sistent with  securing  satisfactory  material,  should  be  so  com- 
prehensive as  to  leave  no  chance  for  ambiguity  or  doubt,  and 
above  all  should  embody  within  itself  the  results  of  the  latest 
and  best  studies  of  the  properties  of  the  material  which  it  covers." 

Unfortunately  the  design  and  construction  of  water-towers  has 
not  always  proceeded  along  lines  identical  with  the  principles 
stated. 

Departure  from  the  rules  of  good  practice  may,  in  certain 
cases,  be  attributed  to  dishonest  motives,,  but  it  is  very  certain 
that  in  the  large  majority  of  cases,  failure  to  make  proper  provision 
for  such  constructive  work  has  arisen  largely  through  ignorance 
both  cf  the  requirements  of  the  structure  and  of  its  constructive 
material  and  workmanship. 

As  has  been  said,  the  inability  to  procure  definite  and  reliable 


298  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

information  as  to  what  does  constitute  a  proper  pra  :tice  is  un- 
doubtedly largely  responsible  for  this  condition  of  Affairs. 

From  the  theories  and  suggestions  preceding,  the  following 
represents  in  a  general  form 


SPECIFICATIONS   FOR    A    STRUCTURAL    STEEL 
WATER-TOWER. 

GENERAL   DESCRIPTION. 

The  structure  will  be  located The 

reservoir  shall  be  a  cylindrical  shell feet  in  diameter  and 

feet  high,  to  be  constructed  of  steel  plate,  riveted  together, 

with  joints  breaking  vertically. 

The  supporting  tower  must  have  a  vertical  height  from  cap- 
stone to  circular  girder  of feet,  and  shall  consist  of  (No.) 

steel  supporting  columns,  divided  into  (No.) stories 

or  panels;  each  panel  shall  include  horizontal  struts  and  diagonal 
tension  rods. 

Columns  shall  be  straight  throughout,  and  incline  from  the 

vertical feet  in feet  (or  column  sections  shall  be 

straight  between  panel-points,  representing  chords  of  a  circle  to 

radius  of feet.  Located  tangent  to  the  vertical  lines  of  the 

tank,  and  upon  the  arc  of  the  circle,  substantial  junctions  shall 
connect  columns;  horizontal  struts  and  diagonals). 

Along  one  of  the  columns  there  shall  be  securely  riveted  at 
appropriate  intervals  a  substantial  steel  ladder,  extending  from 

a  point feet  above  the  capstone  to  opening  in  the  balcony 

floor. 

Each  column  shall  terminate  in  a  suitable  pedestal  and  shall 

be  supported  upon  a (character  of  stone)  capstone, 

to  be  properly  bedded  in  cement  mortar  upon  a  substantial  con- 
crete (or masonry)  pier.  Anchorage  must  be 

provided. 


SPECIFICA  TIONS.  299 

With  each  proposal  there  must  be  submitted  a  stress  diagram 
showing  stresses  to  which  members  are  subjected  and  dimensions 
proposed.  After  award  of  contract,  but  before  materials  have 
been  ordered,  working  drawings  in  detail  shall  be  submitted  to 
,and  shall  receive  the  approval  in  writing  of  the  engineer. 

COVER. 

Surmounting  the  shell  and  secured  thereto  by  angular  steel 
connections,  a  conical  (or  pagoda)  steel-plate  cover  shall  be  con- 
structed. Its  height  shall  be feet  above  the  top  of  the 

cylinder,  and  its  apex  shall  terminate  in  a  conical  steel-plate  cap 
(or  ornamental  galvanized  finial).  The  cover-plate  shall  pro- 
ject  inches  beyond  the  vertical  lines  of  the  shell,  forming 

thereby  an  eave,  terminating  with  a  circular  angle  connection, 
between  which  and  the  shell  shall  be  secured  to  the  cover  a... 

by inch  deep  facia  plate,  with  ornamental  border  (or  for 

facia  plate  describe  galvanized  cornice).      At  a  point  at  the  top 

of   the    shell    an   opening by inches    shall   be   provided, 

reinforced  with  suitable  angles  about  its  under  side  and  supplied 
with  double  steel  doors  securely  hinged. 

LADDER. 

Downward  from  the  metal  doors,  for  a  length  of  . . feet,  a 

steel  ladder,  secured  to  the  shell  at  proper  intervals,  and  capable 
of  sustaining  not  less  than  one  thousand  (1000)  pounds,  shall  be 
provided. 

PAINTER'S  TROLLEY. 

inches  below  the  top  of  the  shell  there  shall  be  firmly 

riveted  a  steel  shape  suitable  for  the  support  of  a  painter's  trolley. 

CIRCULAR   GIRDER. 

The  cylindrical  shell  shall  terminate  in  a  continuous  steel 
plate  girder,  its  lowest  ring  forming  the  web,  to  be  not  less  than 
......inch  thick,  and  to  which  angles  forming 


30O  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

horizontal  flanges  shall  be  riveted.  The  web  shall  be  stiffened 
at  appropriate  intervals  by  vertical  angles  or  other  approved 
shapes  riveted  thereto. 

BALCONY. 

At  some  convenient  point  about  the  circular  girder  there  shall 
be  constructed  a  balcony,  with  floor  of  segmental  steel  plate, 

not  less  than and inches  wide, 

supported  by  steel  brackets,  so  spaced  and  riveted  to  the  girder 
as  to  form  a  substantial  support  for  at  least  five  thousand  (5000) 
pounds  concentrated  load. 

At  a  point  over  one  of  the  tower  columns  an  opening... » 

inches  by inches  shall  be  made  and  reinforced  by  suitable 

angles  about  its  upper  sides. 

At  safe  intervals  upright  steel  shape  posts  shall  be  safely 
secured  to  the  balcony  or  brackets,  forming  the  support  of  a 
substantial  and  ornamental  balustrade  to  be  surmounted  by  a 
suitable  steel  hand-rail inches  above  the  floor-level. 

HEMISPHERICAL   BOTTOM. 

The  bottom  of  the  reservoir  shall  be  riveted  to  the  girder  and 
shall  be  formed  of  special  curved  steel  plate  not  less  than 

inch  thick  and  a  circular  dished  steel  head 

of inch  diameter   of  like  thickness,  and    so    fashioned    that 

when  riveted  together  the  surface  will  form  a  hemisphere. 

INLET  PIPE  AND   CONNECTIONS. 

The  lowest  point  on  the  hemispherical  bottom  shall  be  tapped 
and  properly  reinforced  for  connection  with  a  standard  expansion 

cast-iron  joint  of diameter  and   provided  as  an  inlet 

for  the  cast-iron  bell  and  spigot  supply  main,  which  shall  extend 

feet  vertically  to  and    terminate   in  a  standard   cast-iron 

foot  bend  supported  by  a  substantial masonry  pier. 


SPE CIFICA  TIONS.  301 

The  vertical  supply  pipe  shall  be  further  sustained  by  plate 
steel  collars,  secured  to. .  .inch  radial  rods,  attached  to  each  tower 
leg  in  its  horizontal  plane  and  at  each  panel-point. 

(When  climatic  conditions  render  boxing  or  frost-proofing 
necessary,  insert  the  following:  About  the  vertical  supply  main 

a  frost-case in  diameter  shall  be  provided.  It  shall 

consist  of sections  of inch  plate,  riveted  to 

form  a  steel  tube,  with  horizontal  end  flanges  of 

inch  angles.  In  the  plane  of  each  set  of  horizontal  tower  struts 
(except  when  a  bottom  tie  strut  is  used)  the  pipe  shall  be  braced 

by  means  of inch  collars,  secured  to... inch  horizontal 

radial  rods  extending  to  each  tower  post  at  its  panel-point.  The 
frost-case  shall  extend  the  entire  length  of  the  vertical  supply  pipe 
and  shall  rest  upon  the  pier  supporting  the  foot-bend.) 

The  cast-iron  pipe,  foot-bend,  expansion-joint  (frost-case),  and 
ties  shall  be  included  in  the  cost  of  the  water-tower. 


MATERIALS. 

All  material  intended  to  be  used  in  the  construction  of  this 
water-tower  shall  be  the  product  of  some  well-established  and 
reputable  mill. 

All  tank  plates  and  principal  parts  shall  be  manufactured 
by  the  open-hearth  process  and  the  reduction  of  the  metalloids 
shall  be  insisted  upon  to  the  following  maximum  percentages  in 
the  finished  product: 

Acid  process:  phosphorus 08% 

Basic        "  04% 

Drillings  for  chemical  analyses  may  be  taken  either  from  test 
pieces  or  from  the  finished  product. 

Plate  steel  shall  have  an  ultimate  strength  of  60,000  Ibs.  per 
square  inch,  with  allowable  variation  of  5000  pounds  either  way, 


302  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

as  determined  from  a  standard  test-piece  cut  from  the  finished 
material. 

Cold  and  quench  bends  180  degrees  flat  on  itself  without 
fracture  on  outside  of  bent  portion. 

Broken  samples  must  show  a  silky  fracture  of  uniform  color. 

Punched  rivet-holes,  pitched  two  diameters  from  a  sheared 
edge,  must  stand  drifting  without  cracking  the  material  until 
the  diameter  is  one-third  greater  than  the  original  hole. 

The  ultimate  strength  for  structural  steel  shall  be  the  same  as 
specified  for  plate  metal. 

Finished  bars  shall  be  free  from  injurious  seams,  flaws,  or 
cracks  and  shall  have  a  workmanlike  finish. 

Test-pieces  of  full-size  cross-section  shall  bend,  either  hot  or 
cold,  1 80  degrees  around  a  two-inch  pin  without  cracking  on 
the  convex  surface. 

The  ultimate  strength  of  rod  and  rivet  steel  shall  be  from 
48,000  to  58,000  Ibs.  per  square  inch. 

Test-pieces  shall  bend  180  degrees  flat  on  themselves  without 
fracture  on  outside  of  bent  portions. 

The  rivets  to  be  used  in  this  structure  shall  be  the  output  of  a 
manufactory  having  a  reputation  for  a  superior  product,  and 
the  manufacturer's  test  of  rods  shall  be  accepted  as  sufficient 
by  the  engineer,  but  rivets  taken  at  random  from  any  shipment 
must  successfully  withstand  any  usual  and  reasonable  test  that 
may  be  ordered  by  the  engineer  prior  to  their  use. 

All  rods  requiring  threading  shall  be  properly  "  upset,'1  and 
rods,  nuts,  turnbuckles,  or  clevises  must  be  threaded  to  the  U.  S. 
standard. 

Pins  shall  be  of  material  of  superior  quality  and  shall  be 
accurately  turned. 

INSPECTION. 

An  expert  inspector  shall  be  selected  by  the  engineer  for  the 
purpose  of  testing  the  materials  proposed  to  be  furnished,  and 


SPECIFIC  A  T ION'S.  303 

the  expense  of  mill  and  laboratory  tests  shall  be  paid  by  the  con- 
tractor and  must  be  included  in  the  price  bid  for  this  water- 
tower. 

From  each  lot  of  materials  offered,  one  or  more  samples 
will  be  selected  by  the  inspector  for  testing,  and  all  pieces  intended 
to  be  used  in  the  work  shall  have  the  number  representing  the 
melt  from  which  this  material  has  been  rolled  clearly  stamped 
upon  them,  and  the  absence  of  such  numbers  shall  be  deemed 
sufficient  cause  for  rejection. 

Each  melt  of  steel  must  be  represented  by  test,  and  when 
required,  tests  shall  be  made  of  the  different  sizes  and  shapes 
from  the  same  melt.  Chemical  analysis  of  borings  taken  from 
each  shall  be  made  to  determine  the  amount  of  phosphorus  and 
sulphur  in  the  material  proposed  to  be  furnished. 

Allowance  for  variation  in  weight  shall  be  made  by  the  in- 
spector in  accordance  with  the  standard  adopted  by  the  American 
Steel  Manufacturers'  Association. 

Manufacturers  shall  afford  inspectors  the  usual  facilities  for 
the  examination  of  materials,  which  to  pass  a  surface  inspection 
must  appear  to  be  a  good  merchantable  product,  sound  and 
well  finished. 

Materials  that  have  been  warped  or  buckled  shall  be  rejected. 

If,  for  lack  of  transportation  or  other  cause,  delay  in  shipment 
occurs,  the  material  must  be  safely  stored  and  protected. 

After  leaving  the  mill,  the  right  is  reserved  to  appoint  in- 
spectors both  at  the  shop  and  in  the  field  to  approve  materials 
and  constructive  methods,  but  the  wages  of  such  employes  shall 
not  be  assessed  against  the  contractor. 

STRESSES. 

The  thickness  of  the  plates  composing  the  cylinder  and  the 
bottom  shall  be  such  as  to  sustain  the  stresses  produced  by  their 
weight  and  contents,  with  a  factor  of  safety  of  at  least  four  (4) 


3O4  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

when  computed  by  a  recognized  formula,  with  proper  allowance 
for  decreased  resistance  after  punching  and  riveting,  but  no 
plate  shall  be  less  than  one-quarter  (J)  inch  thick. 

Rivets  shall  be  provided  to  resist  the  entire  stresses  trans- 
mitted, and  shall  be  of  sufficient  size  and  number  to  present  ample 
resistance  to  shearing  and  afford  bearing  area  sufficient  to 
prevent  the  liability  of  crushing  the  metal  about  the  rivet-holes. 
The  bearing  value  of  rivets  shall  be  assumed  at  not  less  than 
twelve  thousand  (12,000)  pounds  per  square  inch  when  the  area 
considered  is  the  diameter  of  the  rivet-hole  multiplied  by  the 
thickness  of  the  metal.  The  pitch  of  the  rivets  shall  equal  the 
net  section  of  plate.  The  ratio  of  the  strength  of  the  riveted 
joint  to  that  of  the  solid  plate  shall  not  be  less  than  the 
following : 

Single-riveted  joint 56% 

Double-riveted  joint 70% 

Triple-riveted  joint 75% 

Double-riveted  butt-welt  joint 87% 

Tensile  and  shearing  strains  on  rods  and  pins  shall  not  exceed 
twelve  thousand  (12,000)  pounds,  and  bending  strains  shall  not 
exceed  twenty-five  thousand  (25,000)  pounds  per  square  inch 
when  the  centre  of  bearings  of  the  strained  members  are  taken 
as  the  points  of  application  of  these  stresses. 

The  stress  in  the  circular  girder  shall  be  assumed  as  due  to 
the  entire  weight  supported  and  the  resultant  horizontal  thrust 
at  the  top  of  the  posts.  The  shear  strain  on  the  girder  and  the 
horizontal  thrust  on  the  lower  flange  ring  shall  not  exceed  ten 
thousand  (10,000)  pounds  per  square  inch  of  metal. 

The  cover  shall  be  designed  to  safely  resist  the  assumed  wind 
stress,  but  no  cover-plate  shall  be  less  than  three-sixteenths  (3/16) 
inch  thick,  and  shall  be  reinforced  when  necessary  by  radial 
rafters,  tie-rods,  or  otherwise. 


SPECIFICA  TIONS.  305 

The  external  pressure  of  the  wind  shall  be  taken  at  and  calcu- 
lations made  for  not  less  than  thirty  (30)  pounds  per  square 
foot  as  exerted  upon  the  vertical  diametral  plane  of  the  tank 
and  exposed  tower  surfaces. 

The  tower  shall  be  proportioned  to  sustain  the  combined 
load  due  to  the  weight  of  the  water,  the  metal  of  the  structure* 
and  the  assumed  wind  pressure  and  resulting  stresses.  Where 
the  main  posts  connect  to  the  tank-shell  the  posts  shall  be  rein- 
forced so  that  the  area  of  section  for  a  distance  of  thirty-six  (36) 
inches  below  shall  be  equal  to  an  area  one  and  one -half  (ij) 
times  the  area  of  the  post. 

The  stresses  shall  not  exceed  fourteen  thousand  (14,000) 
pounds  per  square  inch  for  members  not  exceeding  ninety  (90) 
times  their  least  radius  of  gyration  between  supports,  and  for 
greater  lengths  the  allowable  unit  stress  shall  equal  twenty  thousand 
(20,000)  pounds  minus  seventy  (70)  times  the  length  in  feet 
divided  by  the  least  radius  of  gyration  of  the  section  in  inches. 

No  main  post  shall  exceed  one  hundred  (100)  times  its  least 
radius  of  gyration,  and  no  other  strut  shall  exceed  one  hundred 
and  fifty  (150)  times  the  radius  or  such  length  that  the  fibre 
stress  due  to  bending  from  its  own  weight  shall  exceed  four 
thousand  (4000)  pounds  per  square  inch  of  metal. 

No  shape  weighing  less  than  four  (4)  pounds  per  linear  foot 
shall  be  used  except  for  reinforcement  of  parts  or  for  ornamental 
or  unimportant  features. 

Columns  shall  be  secured  to  steel  base  plate,  reinforced  with 
angle  connections,  and  shall  be  designed  to  resist  vertical  shear 
stresses  not  exceeding  ten  thousand  (10,000)  pounds  per  square 
inch.  The  area  or  bearing  value  of  the  base  plate  shall  be  such 
that  not  more  than  four  hundred  (400)  pounds  shall  be  exerted 
upon  the  upper  face  of  a  monolithic  capstone,  transferring  not 
more  than  one  hundred  (100)  pounds  per  square  inch  to  a  sup- 
porting masonry  pier,  so  proportioned  that  not  more  than 

tons  per  square  foot  shall  be  delivered  to  the  subfoundations. 


306  J^OWERS  AND    TANKS  FOR    WATER-WORKS. 

The  overturning  and  resisting  moment  of  the  water-tower 
shall  be  calculated  from  the  assumed  wind  pressure,  resisted 
by  the  weight  of  the  structure  when  empty,  but  anchorage  shall 
in  all  cases  be  provided. 


SHOP  WORK. 

As  soon  as  received  at  the  shop,  all  material  shall  be  assorted 
and  carefully  and  accurately  laid  out  for  punching,  machiningr 
shearing,  and  rolling. 

Plates  exceeding  three-eighths  (f)  inches  shall  be  planed 
to  a  bevel  by  machining;  all  other  plates  may  be  sheared. 

Plates  under  five-eighths  (f)  inch  may  be  punched  with 
sharp  and  well-conditioned  punch  and  dies  away  from  the  sur- 
faces in  contact.  The  punch  shall  be  one-sixteenth  (1/16) 
inch  greater  diameter  than  that  of  the  rivet  proposed  to  be  used. 

Plates  having  a  thickness  between  five-eighths  (f )  inch  and 
seven-eighths  (j)  inch  must  be  punched  to  correspond  to  the 
diameter  of  the  rivet  to  be  used  and  afterwards  reamed  one- 
sixteenth  (1/16)  inch  larger,  while  plates  exceeding  that  thickness 
shall  be  drilled  from  the  solid  metal. 

In  general  all  bends  in  the  metal  must  be  made  cold,  especially 
in  the  case  of  the  cylinder  and  bottom  plates,  but  detail  pieces 
may  be  bent  hot  without  annealing. 

If  a  steel  piece  in  which  the  full  strength  is  required  has  been 
partially  heated,  the  whole  must  be  subsequently  annealed. 

In  laying  out  plates,  lap-joints  will  be  allowed  only  for  con- 
necting plates  less  than  seven-eighths  (J)  inch  thick;  all  other 
joints  must  be  of  the  butt-strap  type. 

When  "scarfing"  is  necessary,  the  temperature  of  the  re- 
peated metal  shall  not  ,be  more  than  would  be  necessary  to  ignite 
-hard  wood  when  placed  iri  contact. 

c  =  c  JTlanging  or  bending  shall  be  done  by  means  of  suitable  rolls 
and   without   reheating.     This   process   shall   follow   punching 


SPECIFIC  A  TIONS.  307 

and  other  machine  work.  Immediately  after  rolling,  the  several 
parts  shall  be  cleaned  and  assembled  and  all  irregularities  shall 
be  corrected. 

Rivet-holes  shall  be  made  to  coincide  accurately  by  reaming. 

Rivet-heads  must  be  of  uniform  shape  and  size  for  the  same 
size  rivets  throughout.  They  must  be  full  and  neatly  finished 
and  concentric  with  the  rivet-holes.  All  rivets  when  driven 
must  completely  fill  the  holes,  the  heads  being  in  full  contact 
with  the  surface  or  counter-sunk  when  required. 

Whenever  possible,   all  rivets  shall  be  machine-driven. 

All  portions  of  the  work  exposed  to  view  shall  be  neatly  finished 
and  all  surfaces  in  contact  shall  be  painted  with  pure  red  lead 
and  linseed-oil  before  they  are  permanently  connected. 

Columns  and  other  " built"  members  shall,  as  far  as  practi- 
cable, be  completely  riveted  at  the  shop,  leaving  only  connecting 
points,  drilled  to  templet,  to  be  secured  in  the  field.  Important 
parts  shall  be  plainly  marked. 

FIELD   ASSEMBLY. 

Upon  arrival  at  the  point  of  consignment,  care  shall  be  taken 
in  unloading  all  material,  and  parts  damaged  in  transit  shall  be 
rejected  and  promptly  replaced.  All  material  shall  be  properly 
protected  until  ready  for  use.  In  assembling  the  parts,  drifting 
will  be  permitted  only  in  exceptional  cases  and  excentric  holes 
must  be  reamed  and  larger  rivets  shall  be  used  when  required. 

Rivet-calking  will  not  be  allowed  and  loose  rivets  must  be 
cut  out  and  replaced.  Calking  seams  must  be  entrusted  only 
to  skilled  workmen,  using  proper  tools  and  exercising  due  diligence 
to  prevent  injury  to  the  under  plate.  Parts  inaccessible  after 
erection,  and  including  laps  at  joints,  shall,  immediately  before 
being  riveted,  be  given  a  substantial  coat  of  pure  red  lead"  and 
linseed-oil. 


308  TOWERS  AND    TANKS  FOR    WATER-WORKS. 


TEST. 

After  the  completion  of  the  work  the  tank  shall  be  filled  with 
water  and  carefully  tested,  all  leaks  being  noted  and  marked. 
After  emptying,  all  loose  rivets  shall  be  cut  out  and  replaced. 
Leaky  joints  shall  be  made  absolutely  tight  by  calking  only, 
and  all  defective  parts  and  workmanship  shall  be  promptly 
corrected.  Adjustable  members  shall  be  tightened  when  neces- 
sary, and  undue  settlement  of  the  structure  shall  be  remedied. 

PAINTING. 

Following  the  preliminary  test  of  the  work,  all  surfaces  shall 
be  thoroughly  cleaned  and  freed  from  grease,  dirt,  detachable 
mill  scale,  and  rust  by  the  use  of  the  hammer,  chisel,  or  wire 
brush,  and  the  entire  surface  shall  be  thoroughly  dried. 

The  priming  coat  shall  consist  of  a  finely  ground  pigment, 
repellent  to  water  and  mixed  with  pure  linseed-oil.  It  must  be 
applied  as  thick  as  possible,  compatible  with  satisfactory  spread- 
ing. The  paint  shall  not  contain  any  volatile  matter  tending 
to  chill  the  surface  by  evaporation,  and  at  least  twenty-four  (24) 
hours  shall  elapse  before  the  finishing  coat  is  commenced. 

The  material  selected  for  the  finishing  coat  shall  be  one  whose 
essential  principle  shall  be  that  of  an  asphaltic  varnish  and  whose 
preparation  or  manufacture  shall  be  satisfactory  to  the  engineer, 
and  of  such  composition  that  the  under  or  priming  coat  shall  not 
be  softened  or  acted  upon  in  an  injurious  manner.  The  finishing 
coat  shall  be  of  a  different  shade  of  color  from  that  of  the  priming. 

DELAY   IN   COMPLETION. 

In  the  event  the  contractor  shall  fail  to  complete  the  work 
in  the  time  agreed  upon  in  the  contract,  or  in  such  extra  time 
as  may  have  been  allowed  for  reasonable  delays  incident  to  the 


SPEC1FICA  TIONS.  309 

work,  the  engineer  shall  compute  and  appraise  the  direct  damages 
sustained  by on  account  of  the  further  em- 
ployment of  engineers,  inspectors,  or  other  agents,  including 
all  disbursements  on  the  engineering  account  properly  chargeable 
to  the  work.  The  amount  so  appraised  and  computed  shall  be 
deducted  from  any  money  due  the  contractor  under  his  contract. 
The  decision  of  the  engineer  as  to  the  appraisal  of  such  dam- 
ages shall  be  conclusive,  final,  and  binding  upon  both  parties. 


In  awarding  contracts  for  water-towers,  it  is  customary  for 
the  metal  work  and  erection  to  be  separated  from  the  foundation 
work,  the  latter  being  usually  more  economically  undertaken  by  a 
local  contractor  or  by  the  general  contractor,  when  the  tower  is 
an  item  of  other  constructive  work,  as,  for  instance,  a  complete 
water  system. 

Since  the  character  of  the  foundations,  including  capstones, 
depends  largely  upon  local  conditions,  and  as  this  class  of  work 
is  generally  well  understood,  detailed  specifications  for  founda- 
tions are  consequently  omitted.  Attention  is  called,  however, 
to  the  possibility  of  misunderstanding  and  of  accident  resulting 
from  a  division  of  responsibility,  as  evidenced  by  the  failure 
of  a  water-tower  hereinbefore  mentioned. 


CHAPTER  XIV. 
ARCHITECTURE   AND   ORNAMENTATION. 

A  STUDY  of  the  record  of  stand-pipe  accidents  and  failures 
shows  conclusively  the  necessity  for  protecting  such  structures, 
especially  in  icy  latitudes. 

Were  it  not  for  such  object-lessons  directly  appealing  to  the 
utilitarian  sense,  in  view  of  the  little  that  has  been  accomplished 
in  the  past,  it  would  seem  hopeless  to  direct  the  attention  of 
corporations  or  even  municipalities  to  the  splendid  opportunity 
for  ornamentation  and  adornment  offered  by  these  necessarily 
conspicuous  structures  and  sites. 

If  the  need  for  surrounding  steel  stand-pipes  with  a  masonry 
edifice  can  be  demonstrated  as  a  material  element  of  their  safety, 
there  is  a  possibility  that  some  ornamentation  will  suggest  itself 
in  the  design  of  the  masonry  tower. 

Whatever  may  be  said  of  the  past,  there  is  to-day  a  distinct 
and  growing  tendency  toward  civic  adornment,  and  an  increasing 
willingness  to  make  provision  for  the  artistic  along  with  the  useful. 

Dictated  largely  by  a  desire  to  advertise  local  importance 
and  industry  the  great  world's  fairs  have  been  far-reaching  in 
imparting  their  lessons  of  the  true  and  beautiful,  embodied 
though  they  were  in  ephemeral  creations. 

Their  aesthetic  treatment  of  architecture,  enhanced  and  em- 
bellished by  sculpture  and  kindred  arts,  effective  landscape 
design,  with  detail  of  floriculture,  horticulture,  and  forestry,  the 
effect  of  light,  color,  and  the  ornamentation  possible  through 
crystal  jets,  flowing  cascades,  and  pulsating  fountains,  produced 

310 


ARCHITECTURE  AND    ORNA MEN TA  TION.  3 1 1 . 

a,  profound  and  permanent  impression  and  a  broadening  of  the 
artistic  sense  that  has  resulted  in  the  formation  of  such  societies 
and  organizations  as  the  American  League  of  Civic  Improve- 
ment, Architectural  League  of  America,  American  Park  and 
Outdoor  Art  Association,  and  numerous  other  like  parent  bodies, 
each  with  an  ever-extending  realm  of  influence.  In  effect,  the 
movement  is  the  American  Renaissance,  calling  into  life  a  dormant 
instinct  implanted  through  divine  purpose,  prompting  the  beautify- 
ing of  the  ordinary  and  useful,  until  the  instinct  of  the  artist 
shall  have  entered  into  the  conceptions  of  humbler  artisans 
delving  and  fashioning  the  homely  articles  of  commercial  and 
domestic  necessity,  until  as  in  those  older  days  "the  guilds  of 
the  painters  and  sculptors  shall  be  fraternal  to  those  of  the 
weavers,  the  armorers,  the  brewers,  and  the  bakers." 

Until  this  awakening,  a  few  individual  efforts  marked  here 
and  there  a  desire  for  more  beautiful  surroundings. 

L' Enfant  laid  out  our  Federal  capital  upon  broad  and  artistic 
lines,  but  only  since  the  present  century  has  his  careful  and  loving 
efforts  received  their  merited  recognition;  now  a  committee  of 
noted  artists  and  architects  are  devoting  their  talents  toward 
building  the  city  of  his  imagination. 

Marvellous  as  has  been  the  growth  of  industrial  and  scientific 
America  during  the  past  century  in  artistic  cultivation  and  the 
aesthetic  treatment  of  our  surroundings,  as  a  nation  we  are  woe- 
fully behind  those  of  the  Old  World.  Picture  the  Venetian  Cam- 
panile beside  the  wonderful  church  of  San  Marco  and  the  superb 
palace  of  the  Doges.  Only  a  bell-tower,  yet  its  fall  in  1902  shook 
the  world! 

With  this  pride  of  Venice  contrast  the  following: 

From  the  water  of  a  Southern  seaport  city  the  land  slopes 
back  to  a  commanding  height,  and  upon  its  summit,  surrounded 
by  handsome  homes,  stately  live-oaks,  and  overlooking  a  grand 
view  of  harbor  shipping  and  inland  country,  there  rises  a 
gaunt  steel  stand-pipe,  its  faded  sides  tinged  with  yellow  rust 


312  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

streaks  from  innumerable  seams,  and  toward  its  top  the  six-foot 
letters  of  a  real-estate  dealer's  advertisement.  Compare  the 
Campanile,  that  peaceful  home  of  hundreds  of  pigeons,  and  the 
uncrested  stand-pipe,  a  favorite  roosting-place  for  flocks  of  buz- 
zards ! 

The  systematic  design  and  appropriate  ornamentation  of 
masonry  structures  belong  to  civil  architecture,  'the  art  which 
so  disposes  and  adorns  the  edifices  raised  by  man  for  whatsoever 
use  that  the  sight  of  them  contributes  to  his  mental  health,  power, 
and  pleasure";  nevertheless,  so  insensibly  do  in  many  cases 
the  art  and  science  of  architecture  and  engineering  blend,  that 
it  is  a  desideratum  if  not  a  prerequisite  for  the  professed  engineer 
to  understand  and  appreciate  the  principles  of  correct  architecture 
and  to  be  familiar  with  its  fundamental  truths. 

Ruskin  says  there  is  but  one  grand  style  in  the  treatment 
of  all  subjects  whatsoever,  and  that  style  is  based  upon  the  perfect 
knowledge,  and  consists  in  the  simple,  unincumbered  rendering 
of  the  specific  characteristic  of  the  given  object. 

Gerome,  the  great  modern  painter  and  critic,  announces, 
"the  fact  is  that  truth  is  the  one  thing  truly  good  and  beautiful; 
and  to  render  it  effectively,  the  surest  means  are  those  of  mathe- 
matical accuracy." 

Whatever  the  subject,  material,  or  means,  they  must  appeal 
to  the  innate  sense  as  appropriate  to  the  object  sought.  Massive 
weight  must  be  so  supported  that  equilibrium  be  implied;  it 
must  be  apparent  without  analytical  investigation.  An  attempt 
to  trick  the  imagination  through  deceptive  artifices  is  fatal.  Prison 
walls  and  fortress  battlements  should  immediately  convey  their 
purpose  in  grim  and  forceful  character;  the  ornamentation  of 
such  subjects  by  oriental  minarets  or  fanciful  friezes  would 
be  at  once  characterized  as  extraneous,  a  departure  from  the 
truth,  and  hence  false  to  art. 

Discussing  the  design  of  so  simple  a  thing  as  a  doorway,  a 
recent  writer  emphasizes  the  true  and  false  as  follows:  "Between 


. 
ARCHITECTURE  AND    ORNAMENTATION.  313 

colonial  days  and  the  recent  past,  there  was  little  praiseworthy 
in  our  entrances.  With  sudden  wealth  we  treated  huge  blocks 
of  stone  as  though  they  were  of  lace;  gave  fragile  glass  the  air 
of  protecting  a  fortress;  erected  towering  pillars  that  guarded 
doll's  house  doors.  Disdainful  of  harmony  and  proportion, 
we  employed  material  in  a  way  that  was  itself  a  lie.  .  .  .  Do 
not  demand  that  the  «door  shall  tell  of  luxury  within.  You  have 
the  right  to  expect  the  old-time  hinge,  strong  because  it  is  not 
hidden;  welcome  because  it  is  beautiful;  locks,  bolts,  and  nails 
that  are  not  ashamed  to  be  seen;  doors  that  shall  not  be  a  source 
of  pleasure  to  the  present  generation  alone.  Be  prepared  to 
appreciate  harmony  of  design,  even  in  iron,  to  note  how  stone 
and  glass  and  bronze  have  beautified  a  necessity." 

With  architecture  as  with  other  arts  and  sciences  there  are 
simple,  natural  laws  that  must  be  understood;  their  logical 
development  in  architecture  have  created  authenticated  orders 
and  styles,  which  attempt  to  pervert,  modify,  or  amalgamate 
produces  a  lack  of  harmony,  symmetry,  and  repose. 

A  proper  perception  of  these  truths  would  prevent  many 
failures.  Falling  into  this  error,  the  celebrated  architect, 
Christopher  Wrenn,  the  designer  of  St.  Paul's  Cathedral,  London, 
and  many  forceful  and  beautiful  architectural  examples  of  the 
seventeenth  century,  departed  from  the  "Gothic  rudeness"  of 
splendid  Westminster  Abbey,  and,  attempting  to  introduce  addi- 
tional wings  of  "good  Roman"  style,  perpetuated  a  failure  as 
the  result  of  an  attempt  to  compel  the  union  of  opposite  orders, 
classic  in  themselves,  but  unartistic  and  inharmonious  in  their 
combination. 

Such  deviation  from  the  principles  of  correct  architectural 
style  are  too  abundant.  Consider  the  design  of  one  of  the  prin- 
cipal buildings  of  the  Louisiana  Purchase  Exposition.  In- 
tended as  a  building  for  housing  exposition  exhibits,  "it  was 
argued  that  it  should  express  externally  as  much  friendly  dignity 
as  would  be  compatible  with  its  ephemeral  character;  that  it 


3 1 4-  TOWERS  AND    TANKS  FOR    WATER-WORKS. 

would  be  incongruous  to  disguise  this  character  under  the  garb 
of  severe  and  classic  forms  which  we  associate  with  the  most 
lasting  architectural  monuments  of  antiquity;  and  that,  further- 
more, being  a  part  of  the  greatest  exposition  ever  attempted,  it 
should  undoubtedly  be  novel,  striking,  and  full  of  life." 

Proceeding  upon  these  lines,  a  building  was  designed  con- 
cerning which  its  architect  says:  "Some  have  attempted  to 
classify  it  as  an  example  of  the  'noveau';  but  when  I  recently 
noticed  an  English  art  critic  say,  in  protesting  against  its  invasion 
of  Great  Britain,  that  this  'noveau'  art  is  'a  malady  the  pernicious 
virus  of  which  becomes  more  acute  the  further  it  travels,'  I  feel 
a  strong  personal  solicitude  for  a  properly  conducted  baptismal 
ceremony.  Let  us  therefore  name  it  'Secession  Architecture.' 
Perhaps  I  will  have  to  explain  what  secession  architecture  is,  if 
the  name  should  not  make  it  quite  clear.  It  means  architectural 
liberty  and  emancipation  with  a  strong  plea  for  individuality. 
It  is  a  breaking  away  from  conventionality  of  design;  it  is  more 
an  architecture  of  feeling  than  formula.  Editorially  commenting 
upon  the  building  and  the  explanation  of  its  author,  one  of  the 
technical  papers  says:  'If  we  were  to  engage  in  speculation  as 
to  the  style  of  architecture  which  this  remarkable  design  repre- 
sents, we  would  suggest,  as  Ionic  pilasters  and  Doric  columns 
unite  to  support  a  Spanish  roof  surmounted  by  a  dome  of  Renais- 
sance effect,  while  Egyptian  monoliths  guard  the  entrance  to  a 
doorway  ornamented  by  Grecian  fretwork,  and  a  number  of 
additional  styles  have  evidently  '  felt '  their  way  into  the  composi- 
tion, it  would  be  more  appropriate  to  call  it  mongrel  architecture. 
To  attempt  to  succeed  by  departing  from  all  recognized  laws  of 
artistic  design  may  result  in  '  novel  and  striking  forms,  but  noth- 
ing can  be  produced  in  this  way  which  will  receive  the  world's 
admiration  as  did  the  famous  'White  City'  on  the  shore  of  Lake 
Michigan." 

Possibly  with  the  memory  of  some  such  atrocity  of  design  or 
with  prophetic  vision,  a  few  years  since  the  Engineering  Record 


ARCHITECTURE  AND    ORNAMENTATION.  31$ 

asked  for  competitive  designs  of  water-towers  and  power-stations, 
and  referring  to  builders  of  water-works,  editorially  announced: 
"The  projectors  of  such  enterprises  should  not  erect  structures 
placed  on  hill-tops  to  be  an  offence  to  the  eyes  of  this  and  future 
generations. 

"The  additional  expense  of  beautifying  these  structures 
need  not  be  great  if  the  design  and  execution  be  entrusted  to 
competent  architects.  The  necessary  isolation  and  altitude  of 
these  buildings  is  at  once  a  suggestion  of  the  availability  of  the 
site  as  a  pleasure-ground,  the  tower  itself  constituting  an  admirable 
central  feature  readily  adapted  to  the  purposes  of  a  lookout. 

"In  the  case  of  private  ownership  it  should  be  borne  in  mind 
that  in  the  bestowal  of  such  franchises  the  community  gives, 
without  price,  something  of  substantial  value,  which  might  grate- 
fully be  in  part  repaid  by  the  avoidance  of  an  absolutely  ugly 
sore  on  the  landscape  at  least,  if  not  by  throwing  open  to  public 
enjoyment  something  of  the  nature  of  la  public  park." 

In  passing  judgment  upon  a  number  of  prize  designs,  a  well- 
selected  committee  of  architects  and  engineers  say  in  part: 
"The  conditions  under  which  we  were  invited  to  act  were,  first, 
adaptability  for  the  purpose  desired;  second,  architectural 
design;  third,  economy  in  the  treatment;  fourth,  rendering  of 
the  drawings.  In  interpreting  these  conditions  we  were  led  to 
believe  that  the  general  scope  and  intent  of  the  competition  would 
lead  to  precedence  being  given  to  adaptability  rather  than  to 
merely  artistic  expression  in  the  design,  and  that  in  considering 
the  merits  of  the  various  designs  submitted,  other  things  being 
equal,  the  design  given  the  higher  place  should  be  based  upon 
ordinary  and  feasible  conditions,  such  as  might  arise  in  the  average 
community,  rather  than  upon  exceptional  or  unusual  conditions, 
even  if  exceeding  in  artistic  merit. 

"We  regret  that  so  few  designs  were  presented  in  which 
artistic  effect  had  been  sought  by  simple  means,  rather  than  by 
costly  and  formal  architectural  devices.  It  must  frequently 


316  TOWERS  AND    TANKS  FOR    WATER-WORKS. 


TOWER  TO  BE  BVILT  OP  LOCAL  STONE,  WITH 
<MP  A  DARKER    COLOR  "- 


FlG.   60.  —  "ENGINEERING    RECORD"    FlRST   PRIZE,    WATER-TOWER    DESIGN. 


FIG.  61. — ST.  Louis  WATER-TOWER. 


(To  face  page  317.) 


• 
ARCHITECTURE   AND    ORNAMENTATION.  $17 

occur  in  the  execution  of  work  of  this  kind  that  the  money  at 
command  is  limited,  and  the  simplest  possible  architectural 
expression  is  the  only  thing  possible.  Consistent  with  this  fact, 
we  have  awarded  the  first  prize  to  a  design  which  would  give 
valuable  suggestion  to  communities  of  moderate  means  called 
to  erect  structures  of  this  sort." 

A  recently  constructed  masonry  structure  about  a  steel  stand- 
pipe  and  a  part  of  the  St.  Louis  water-works  system  is  a  fair 
example  of  possibilities  in  this  connection.  As  may  be  seen 
from  the  accompanying  illustration  (Fig.  61),  the  circumscribing 
edifice  is  costly,  massive,  and  imposing,  and  ornamental  to  the 
vicinity  in  which  it  has  been  erected.  As  a  whole,  its  effect  is 
pleasing,  but  it  is  to  be  regretted  that  a  more  appropriate  roof 
design  had  not  been  provided.  The  bell-shaped  superstructure 
has  a  " beehive"  appearance,  which  detracts  from  an  otherwise 
fine  type  of  water-tower  construction. 

A  steel  water-tower  is  a  much  more  promising  problem  for 
architectural  beauty  than  its  companion,  the  cylindrical  stand- 
pipe,  since  in  that  direction  opportunity  is  limited  to  correct 
construction  and  taste  displayed  in  detail  and  painting.  A 
worthy  example  of  what  may  be  done  with  such  a  structure 
is  the  water-tower  designed  by  Prof.  Marston  for  the  Iowa  State 
College,  hereinbefore  mentioned  and  illustrated  in  Fig.  62.  Its 
purpose  is  unmistakable,  its  lines  are  graceful,  and  the  effect 
altogether  substantial  and  pleasing.  Analogous  to  the  limited 
possibility  of  architectural  effect  in  water-tower  construction  is 
the  modern  steel  bridge,  concerning  which  Mr.  Alfred  P.  Boiler, 
M.  Am.  Soc.  C.  E.,  in  his  work  on  "Highway  Bridges,"  says: 

"In  the  true  sense  of  the  term  architecture,  unadorned  con- 
struction is  as  much  a  part  of  architecture  as  the  more  popular 
idea  that  it  simply  covers  the  art  of  producing  pleasing  effects. 
A  man  cannot  be  a  good  architect  before  he  is  a  good  construc- 
tionist,  no  matter  how  dexterous  he  may  be  in  devising  graceful 
forms  or  artistic  in  his  selection  of  colors.  In  bridge-building 


TOWERS  AND    TANKS  FOR    WATER-WORKS. 

there  is  little  room  for  artistic  architecture,  and  any  pleasing 
effect  produced  must  grow  out  of  consistency  of  design  and  a 
thorough  knowledge  of  the  peculiarities  of  materials  of  construc- 
tion and  color.  To  an  educated  person,  correct  construction 
always  produces  a  sense  of  satisfaction,  for  in  it  is  involved  the 
idea  of  proportion  and  appropriateness  for  the  service  to  which 
it  is  put.  Concealment  of  constructive  forms,  by  mouldings, 
panels,  or  other  devices,  to  suggest  something  else  than  what 
the  construction  really  is,  is  vulgar  as  well  as  dishonest.  To 
construct  a  girder  bridge  and  give  it  the  appearance  of  being 
an  arch  illustrates  what  is  here  meant  by  falsity  of  architecture, 
specimens  of  which  more  than  one  of  our  public  parks  contain. 
Possibly  to  bridges  more  than  to  any  other  class  of  public  works 
does  the  Ruskinian  axiom  (which  cannot  be  repeated  too  often) 
apply:  'Decorate  the  construction,  but  not  construct  decoration.' 
Such  a  principle  conscientiously  kept  in  view  cannot  but  result 
in  else  than  good  work.  Its  violation  results  in  a  senseless  fraud 
demoralizing  to  the  taste  of  the  community  where  such  violations 
may  occur.  Public  works,  in  a  certain  sense,  play  a  part  in  the 
education  of  a  people,  and  their  authors  and  builders  have  con- 
sequently to  that  extent  a  responsibility  in  addition  to  the  mere 
utilitarian  idea  of  endurance  and  safety.  The  ideas  herein 
advanced  are  not  novel  ones  by  any  means;  but  they  cannot  be 
enforced  too  often,  when  in  this  boasted  age  of  culture  and  civiliza- 
tion a  community  will  permit  the  huge  architectural  fraud  of 
the  Fairmount  Bridge  over  the  Schuylkill  at  Philadelphia,  and 
hardly  yet  completed.  Constructively,  this  bridge,  with  its 
double  tier  of  floors,  spanning  the  Schuylkill  in  a  single  stretch 
of  340  feet,  is  a  monument  to  its  designer  and  an  honor  to  American 
engineering.  Instead  of  letting  the  enormous  trusses  stand  in 
all  their  grandeur,  depending  wholly  upon  judicious  painting 
and  the  design  of  the  cornices  and  railings,  etc.,  for  their  aesthetic 
effect,  thousands  of  dollars  have  been  spent  in  actually  covering 
up  the  trusses  to  a  great  extent  with  -sheet  iron,  forming  an  arcade 


FIG.  62. — AMES,  IOWA,  STEEL  WATER-TOWER. 

(To  face  pa?e  318) 


. 


ARCHITECTURE  AND    ORNAMENTATION.  319 

as  it  were  of  great  massiveness  by  arching  between  the  posts 
of  the  trusses,  the  arches  springing  from  large  Roman  sheet- 
iron  capitals  about  hall-way  down  the  posts.  The  result  is  that 
at  a  little  distance  the  spectator  beholds  an  arcade  without 
any  visible  means  of  support  for  a  distance  of  340  feet.  To  be 
thoroughly  consistent,  the  architect  (Heaven  save  the  name !)  of 
this  constructed  'decoration'  should  have  at  least  sanded  his 
sheet  iron  when  painted  and  marked  out  in  strong  lines  the  joints 
that  masonry  of  similar  forms  suggests. 

"  About  one  mile  north  of  this  bridge  a  noble  structure  spans 
the  Schuylkill,  the  Girard  Avenue  Bridge,  as  it  is  called.  As 
an  engineering  accomplishment  it  stands  in  no  comparison  with 
the  bridge  at  Fairmount,  the  spans  being  much  smaller,  and 
only  a  single  roadway  (of  paved  granite)  is  carried  on  the  upper 
chord,  it  being  a  'deck  bridge.'  Architecturally  it  is  certainly 
one  of  the  finest,  if  not  the  finest,  bridges  in  America;  while  in 
the  same  sense  the  Fairmount  bridge  is  the  worst,  and  probably 
the  worst  in  the  world.  The  Girard  Avenue  is  an  example  of 
pure  decorated  construction,  and  the  writer  is  aware  of  no  place 
in  this  country  where  the  principles  for  which  he  has  been  con- 
tending can  be  so  well  illustrated  as  in  the  case  of  these  two 
Philadelphia  bridges." 


INDEX. 


ARCHITECTURE: 

Competitive  Water-tower  Designs,  315. 
Examples  of  Water-tower  Design,  317. 
Incongruous,  313. 

Ornamentation  of  Metallic  Structures,  317. 
Ornamentation,  opportunity  for,  316. 
Style  in,  312. 

Tendency  toward  Improved,  311. 
CAPACITIES: 
Cones,  in. 
Cylinders,  in. 
Hemispheres,  112. 
Segment  of  Sphere,  112. 
Tanks,  92-99,  163. 
COLUMNS: 

Gordon's  Formula,  105-106. 
Sections,  216. 

Straight-line  Compression  Formula,  107-108. 
Stresses  in,  i35-i38>  2I3~2I5- 
DETAILS: 

Anchorage,  173,  203-205,  218-219,  236-241. 

Bearing-plate,  218. 

Bed-plate  and  Connections,  170. 

Balcony,  200. 

Circular  Girder,  188-191,  207-209. 

Connections,  202. 

Discussion  concerning,  171-172. 

Estimating  Quantities,  205-207. 

Frost-proofing,  200. 

321 


3 22  INDEX, 

« 
DETAILS: 

Graphic  Design,  205. 

Ladder,  198-199. 

Supporting  Tower,  192-194,  196,  216-217. 

Tank  Bottom  and  Connections,  184-188. 

Tank  Cover,  197-198. 

Trolley  Rail,  198. 

Wind-bracing,  203. 
ERECTION: 

Delivery  of  Materials,  281. 

Foundations,  208. 

Field  Assembly,  282-284. 

Field-riveting,  285-286. 

Inspection,  284. 
FAILURES: 

Atlantic  City,  N.  J.,  16. 

Classification  of,  51. 

Cortland,  N.  Y.,  15. 

Elgin,  111.,  20. 

Fairhaven,  Mass.,  16,  179-184. 

Garden  City,  Kan.,  14. 

Griswold,  la.,  u. 

Lena,  111.,  12. 

Lincoln,  Neb.,  28. 

Normandy  Heights,  Md.;  30. 

Red  Oak,  la.,  12. 

Waco,  Tex.,  16. 
FORCES: 

Bending  and  Resisting  Moments,  101. 

Equilibrium,  81. 

Hydrostatic  Pressure,  88-90,  162. 

Moment  of,  80. 

Moment  of  Inertia,  101-102. 

Modulus  of  Elasticity,  102-104. 

Overturning  Moment,  211. 

Resistance  to  Overturning,  81-88,  219. 

Resistance  Offered  by  Materials,  90-91. 

Radius  of  Gyration,  104. 

Tension  on  Joints,  212. 

Tortion  Moment,  210. 


INDEX.  323 


FORCES  : 

Wind -pressure,  82-84,  133,  209. 
FOUNDATIONS: 

Bearing  Values,  224-226. 

Clay,  221. 

Concrete,  232-233. 

Dry  Sand,  223. 

Designing,  236-242. 

Masonry,  226-232. 

Maximum  Pressures,  233-235. 

Preparation  of,  280-281. 

Quicksand,  224. 

Rock,  220. 

Stresses  in,  139-140. 
INSPECTION: 

Steel,  74-78,  284. 
MASONRY: 

Brick,  229-231. 

Concrete,  232-233. 

Stone,  226-229. 

Weights  of  Stone,  242. 

Weight  of,  236. 
PAINT: 

Asphaltic  Varnish,  262-265. 

Application  of,  265-268. 

Average  Surfaces  Covered  by,  275. 

Chemical  and  Galvanic  Action,  245-249. 

Discussion  of,  243-244. 

Films,  255-258. 

Iron  Rust,  244. 

"Japanned"  Plates,  254-255. 

Mill-scale,  246-247. 
"Oxidized"  Plates,  254. 

Pigments,  258. 

Preparation  for,  250-253,  279. 

Practical  Considerations,  255. 

Protective  Coverings  Discussed,  268-274. 

Red  Oxide  of  Lead,  258-260. 

Zinc  Coating,  253. 


324  INDEX. 

RIVETING: 

Double-riveted  Joint,  147-148. 

Double-welt  Butt-joint,  149-152. 

Field  Riveting,  285-288. 

General  Practice  in,  142-143. 

Joint  Efficiency,  144-169. 

Pitch  of,  155. 

Size  of,  156-161. 

Single-riveted  Joint,  144-147. 

Steel  Rivets,  154. 

Triple -riveted  Joint,  148-149. 
SHOP  PRACTICE: 

Assembly,  279. 

Cleaning  and  Priming,  279. 

Laying  Out,  276. 

Machining;  Punching  and  Rolling,  277-278. 
SPECIFICATIONS: 

Application  of  Paints,  265. 

Brick  Masonry,  229. 

Concrete,  232. 

Cleaning  Metal,  250. 

General  Discussion  of,  289. 

International  Association,  47. 

Manufacturers'  Standard,  for  Steel,  45. 

Repainting,  268. 

Steel,  Physical,  68. 

Steel,  Chemical,  73. 

Stone  Masonry,  228. 

Stone  Monoliths,  241. 

Stand-pipes,  8,  10,  u,  12,  15,  16,  20,  28,  30,  298-308. 
STEEL: 

Bessemer,  40. 

Chemical  Specifications  for,  73-74. 

Comparative  Cost  of,  58. 

Comparative  Strength  of,  59. 

Difference  from  Iron,  36-38. 

Distinguishing  Terms  of,  65-68. 

Effect  of  Heating,  39. 

Effect  of  Phosphorus,  42-44. 

Inspection  of,  74-78. 


INDEX.  325 

STEEL: 

Manufacturers'  Specifications  for,  45-47. 

Open-hearth,  41. 

Report  of  International  Association,  47-49. 

Relative  Merits  of,  52-58. 

Rivets  of,  154. 

Stand-pipes  of,  5-9. 

Suitable  Grades  of,  61-65. 

Specifications  for,  68-73,  3O1- 

Thickness  of  Plates  of,  91,  166-167, 
STRAIN- SHEETS: 

163-165,  206. 
STRESSES: 

Compression,  79. 

Explanation  of,  79,  109. 

Foundation,  139-140,  215,  233-236. 

Gravity,  109. 

Horizontal,  132-133. 

In  Cylinder,  112-114,  134- 

In  Cone,  114-116. 

In  Circular  Girder,  120-127,  207-209. 

In  Joint,  117-120,  212. 

In  Posts,  127-128,  213-215. 

In  Segment  of  Sphere,  116. 

In  Ring  at  Top  of  Posts,  130-132. 

In  Tower,  135-139,  213-215. 

Resulting  from  Horizontal  Thrust  at  Top  of  Posts,  128-129,  210. 

Shear,  79-80. 

Tension,  79. 

Wind,  133-139. 
WATER-WORKS: 

Ancient,  Examples,  i. 

Gravity  Systems,  2. 

Reservoirs  for,  3,  5,  10,  162-163,  177. 


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